Computer won't boot - motherboard, processor or PSU?

[träskmannen]

My computer decided to play a little prank on me yesterday evening and chose not to boot anymore. The last time I used it (the day before that) everything was fine. It was shut down OK. Nothing new installed, neither internal nor external.

When I try to start it the case fan and the CPU fan will work. The light in front of the case as well. The diode on the motherboard lights up. That's it - it won't get any further. No beep (there used to be one...) and it won't enter BIOS. The screen remains black (no signal). The screen works and I have of course checked that all cables were connected before going further. If I press and hold the power button again it will shut down (as usual).

I have checked the BIOS battery (voltage OK), reset the BIOS - still no change. Unplugged all hard drives and optical units - no change. Unplugged all connections to the case (front USB ports etc) - same story. Removed the capture card and graphics card - still no change. Removed the memory as well - no improvement. The motherboard is not in electrical contact with the case.

That leaves me with a PSU, a motherboard and a processor, and that's how far I have come in the troubleshooting. I have measured the output from the PSU and it seems OK although the voltage is a bit on the high side, roughly 0,5 V higher than nominal (for instance 12,5 V on the yellow cables that should be 12V. That might be due to my multimeter being both old and cheap, just like me.)

It is a bit too expensive for me to replace both motherboard, processor and PSU right now, is there any good way to narrow it down further? I have no computer with similar components so I cannot exchange parts to see which one is faulty.

Does anybody have a good idea about how to continue?

[mh2360]

It could be just one or all three components that are faulty, you really do need a way to test them all.

If I was a betting man, i'd say it was the CPU. Dead CPU's i have seen in the past cause the same behaviour as you describe - Fans and lights work, but thats all.

I could be wrong however.

[MikeV]

Check the -12v and -5v from the power supply, if they are missing or low the computer will not boot.

[t0nee1]

Had same prob. it was the PS, does it smell burnt? not enough juice to power up mobo...... I'd start there....

[Bjs]

A: Check reset / start buttons on case are working , CORRECTLY .

If these start playing about , they can cause all sorts of weird crap to happen .
Check that these buttons , and associated cabling show no signs of melting , it used to happen on poorly made cases .

B: Change / swap the keyboard / mouse , I joke you not .

I have seen complete and utter useless , garbage keyboards cause such issues in the last few years .
Even the cheapest microsoft keyboard / mouse is far superior to all others , unless you can afford to go with logitech .

Just dont install the rotten software that comes with them , esspecially microsofts rubbish .

C: Take the psu and throw it in the bin , and go get one rated above 450watts , and try again .

You can measure it all you want with nifty measuring gadgets , but it will only show its true colours under load , physically loaded by the hardware , where the fault will be detected .

Hopefully , this is the problem , and your back up and running .

----

Come on dell , quit it with those under power p4s ...

----

Make sure you also use atleast a basic power board for the pc , one that comes with active spike protection , their cheap , but reasonably affective .

No improvement ?

D: Strip it

Basics are psu , case , keyboard (ps2) , motherboard , memory , cpu , start and reset buttons must be connected as they form part of the system pre-check .

Fire it up , it must beable to atleaset give the post beep .

Nothing ?

Then it most likely comes down to taking the cpu out of the motherboard and taking a look at it , from the pins side .

If you see anything that looks like a film of fluid anywhere near the pins , looks a bit like singer sewing machine oil , or baby oil , then the incorrect heat sink compound was used , and you may find your up for another motherboard , but I would seriously consider replacing both , including the cpu . Just make sure it matchs the memory chip/s you have .

Cleaning the modern cpu is a delicate job , and done with care , and caution , but still not guaranteed .

I have seen systems rescued from this point , and you might get lucky , but in my experience , its not worth the hassles from the customers point of view , because it can do two things .

A: Behave and show no problems (or relatively minor ones).
B: Be the worst perfoming system ever rebiult , and deserves a place in the bin .

That would be about it , apart from your remark .

"I have no computer with similar components so I cannot exchange parts to see which one is faulty. "

Yes , it makes it easier , but havent the cpu sockets gone through some changes in the last few years , and memory as well .

Good old days of the super socket 7 , then intel decide no more and messed the whole picture up for good .

[träskmannen]

Thanks for the tips and ideas, all of you. I decided to use the age-old tactics "go for the cheapest first" so I bought myself a new PSU. Unfortunately that didn't help. Two to go now...

@Bjs:
A) is OK (measured and tested)
B) Definitely OK. I am using the same keyboard / mouse right now (logitech) and that is no problem.
C) Done (although I won't throw it away since it seems to work OK after all, the replacer gave the same problems)
D) Stripped. No beep, no signs of intelligent life at all. The fans move some air and that's it.

CPU looks the way it should, no greasy film anywhere.


I think will get a new motherboard and a new processor at the same time. I have the possibility to return an un-opened box and get the money back so I will try with one of them first, and see if that helps. If not, then I was out of luck. Does anyone have a bright idea about what to try first? Is there a risk that a faulty motherboard will fry a new processor if I try to exchange that one first? Or vice versa?

[redwudz]

I have a similar situation. Fans work, CD tray ejects, but no beeps, no HD spin up and black screen. I have a dead PC because a USB socket shorted out. The PS is fine. I tried a spare CPU with the motherboard and had the same result.

But I risked killing a known good CPU. Generally when a CPU dies, it just destructs internally and a dead one shouldn't cause any problems to a motherboard. The other way around such as I did is more risky to a CPU. Even then, it's much more common that a dead motherboard is because of a open circuit, not a short. If it was shorted, the PS should have blown a fuse or failed. Always exceptions, though.

When you pull the MB out of the case, check closely for any overheat or burn marks, both sides, and all sockets for any signs of heat. That may give you a clue. Most of the time, there is nothing obvious, though.

I'll replace the MB, then try the old CPU. If that doesn't work, I'll try the slower spare CPU. At that point I'll know if there is any damage. If it is the CPU, then hopefully the RAM and everything else survived.

You do want to throughly check all wiring and connectors before mounting and powering up the new MB. When you first power on, if you don't hear the beep right away, turn it all off and re-evaluate.

Good luck with your problem.

[Patricks]

Hi Traeskmannen,

I suggest that you, before going for a new mobo or a new cpu, try
the following.

1) get (borrow) a 100%-sure working graphic display card
2) disconnect power to the mobo & remove the button battery
from the mobo. You mentioned your measuring the voltage
of the battery (I guess that you meant while it was still sitting
on the mobo) and your resetting the BIOS (I guess you meant
removing or inserting a jumper on the mobo).
3) Remove/disconnect devices (e.g. capture card, floppy drive,
etc) connected to the mobo. Reinsert the button battery.
Just insert the 'sure' working graphic display card and connect
signal cable of monitor to the display card. Then apply power ..
4) Sometimes, static charge may cause "flip-flops' to behave
unpredictably. On several occasions, I was able to boot up
the computers again by reinserting battery together with
swapping display card.

Good Luck !

[TBoneit]

In my experience Motherboard. if an E-Machine then Motherboard and Power supply. With No memory or Video card it should beep beep beep etc. error code. OTOH dead CPU/PS/Mobo no beep. You changed the PS. Pull all the cards, Memory cables to drives and still no beep try the Mobo first. They are much more likley to go than the CPU. Don't forget to clean the surface between the CPU and the Heatsink and apply new Thermal compound.

I need to take one of my computers to work and redo the Thermal compound as lately the cpu fan has been surging. This makes me suspect that the compound is at the end of its life and not providing 100% contact. I'll probably take some blank DVDs too, blow out the windows and reload too.

[DarrellS]

My brother had the same problem when he built his computer except that it never started. He thought it was the power supply and bought another one but still no go.

We checked the ASUS website and they said to test the board outside the case with everything connected to see if we had a bad case so we took it to frys and they tested it for us. The board was fine so he bought another case and the computer has run fine ever since.

[träskmannen]

Problem is finally solved. Thanks again for all the tips, hints and ideas. I have considered most of them, tried the ones I could but to no avail. It turned out to be the motherboard that was malfunctioning. Unfortunately I tried the processor first (I was lazy) so I ended up exchanging both PSU, motherboard and CPU. Shit happens, I guess. Annoying - that system was only half a year old. Well, I got to learn a bit more about troubleshooting and I ended up with a faster processor than I started with so I got something out of the experience anyway.

[Nelson37]

I agree with sequence, unplug everything, power supply, then motherboard, then CPU.

I have seen both CPU-Killer motherboards and MOBO-Killer CPU's. The problem is that confirming this requires frying another known good component. Damn, the mobo really IS frying processors! Sumbitch! Get me another one of them there chips, Billy-Bob! And a new board, too.

While I have seen cases cause a short, in one case with the opposite side lid on rather than off it would short, take the side panel away from the motherboard off and it ran fine. Installing panel flexed the rear of the case and made contact.

At only six months you should still be under warranty. The process you have gone through should provide absolute proof even for individual component warranty.

[redwudz]

I was sort of lucky with my dead PC. It was the motherboard. Good news is that everything else is OK. I just finished installing a new MB and stuff, all in a new case, without the problematic USB PCI sockets. This MB has 4 USB sockets at the rear and 2 on the front of the case. I also installed a media card reader which has an additional USB socket.

This was all caused by a cheesy USB socket. The separator broke off in the socket and when I went to plug the cable back in, it bent the 5VDC lead down against the metal part of the socket. Apparently that overheated the USB circuitry in the MB and killed the MB. When I removed the USB PCI socket, I could clearly see where the lead was touching the socket. My luck it was the 5VDC lead, not the ground or data leads.

Oh well, only about $50US for the new MB. It could have been worse.

[TBoneit]

I've got a laptop with two bad USB ports myself. Fortunately they didn't short out anything before I noticed them. I have now filled them with hot melt glue and just use the other 4.

I had one customer kept killing USB ports on a ASUS mobo. They were fine until he plugged in his HP All in one. He Warrantied it. No more problem.