Help with motherboard or power problem

[koinhelgo]

OK Here are the details.........
I was given a friends pc to look at a problem hard drive. Upon boot it could not recognise drive or said there was no system, even though it would display contents after booting to DOS with a floppy.
When I got the pc home and turned it on, after about 10 secs it shut off and almost immediatedly turned back on again and started to boot- then the fail message. I thought perhaps it was just a "feature" of his pc.
I took out the drive and noticed the drive was set to cable select, which I changed and put it in a spare machine I have, as a slave. Did checkdisc etc and the drive seemed to be OK and the files were accessable
When I put the drive back (as master) in the pc and switched on, the pc started switching on and off rapidly. I switched off again and checked all connections and gave it a general clean and reseated all cables etc, including the leads to the mobo from the front panel (power switch, power LED and speaker, I think). The mobo pins for the power switch connector looked a bit bent but straightened when I reseated the connector and it seemed to give a better connection.
Upon restart the pc powered up and booted into the XP log on screen then switched off again. The front power switch then wouldn't turn on the machine. I pulled out the power cord and put back in again and the power switch worked again. The next time I got into XP but after about
five minutes it switched off once more, again I had to unplug the power chord and put back in again to get power switch to work.
After a few goes where the pc switched itself off and on again rapidly, I again got it to boot but after another five minutes it switched off again.
At this point I had to give up and go to work.
This seems to be a power issue and I suspect the mobo connections to the power switch or perhaps there's a short on the board- because I did (dangerously) decide to pull out the connector when the pc was switching itself on and off and it made no difference to the machines behavior.
However as the pc usually wont come on until I pull out the power chord and plug back in again could the PSU be fawlty or is it just needing "reset" after a power problem.
My friend says it never displayed this behavior before- only the hard drive problems. He did have it in the back of his car for a week before he gave me it and I had it in my boot to take home so maybe that has caused some damage.
I have a new PSU to fit to my pc (not enough grunt in old one to pwer all I have attached plus a new gfx card I've just got) and so will hopefully be able to fit my old PSU to his machine to test this (although I will have to get a 24 pin to 20 pin adapter).
The cpu fan seems to be working OK and heatsink looks well seated, it is a 1.8 Celleron with only 128 meg of PC2100 RAM, although I fitted two 256 meg PC2100 sticks I have and it still switched off etc. It has no graphics card the mobo doesn't even have an AGP slot. The HDD is a Seagate 40 gig installed as master on Primary IDE and a a DVD Burner (NEC 3520) installed as master on Secondary IDE. Running XP Home SP2.
That's all the info I can think off (don't know the mobo brand etc and can't look at the moment). I would appreciate any thoughts or help anyone can offer.
Regards

[rkr1958]

I quickly read through your post and if I make a suggestion, or ask a question, that you've already covered please disregard.

1. Have you tried booting up without the harddrive or any other IDE (or SATA) drives connected? What happens.
2. Did you added the two sticks of 256MB PC2100 RAM to the one stick of 128MB PC2100 RAM? If so, what happens when you take out the 128 stick and replace it with one of your 256MB sticks or RAM and reboot (without) the harddrive?

[koinhelgo]

I took outh the 128 stick completely and put in both my 256 meg sticks, so it aint the RAM that is at fault- i did consider a fawlty Ram slot but I don't think this would make the power switch rapidly on and off like it did.
I tried another hard drive with the system but it didn't want to boot to xp with the difference in hardware being too much for it, just pegged back to screen asking if I wanted to try and load windows normally or not.
I have just got hold of a blank 20 gig drive today and will try installing that in the system tomorrow after my night shift to see what happens.
I did switch on the pc without the burner connected but it still displayed the problems.
Didn't think to switch on with no HDD and see if it lasted or not.
The only other thing is the PSU is only 145 W, so it's pretty poor anyway.
Regards

[Nelson37]

Power Supply is so cheap and easy to replace just put in a new one and test. Or, use the one from your PC and just hook up the power leads to test that.

Highly unlikely the drive would be the problem cause if it shorted then it would have done the same in your PC.

Could be the PS is marginal and the drive using slightly more than normal amount of power, either way the fix seems to be a different PS.

If it still reboots, then make sure all drives and cards are disconnected, both data and power cables, even remove the RAM and let it sit with the fans spinning. If that reboots, Its either Mobo or chip, neither one is cost-effective to replace with compatible units, it will be upgrade time!

[Headbanger's Ball]

My guess is a bad power supply. Swap it out with the one from your pc & try.

If the same thing happens with a good power supply, check the cpu fan.