I bought recently External Pioneer DVD burner DVR-106D with firewire.
I'm having a strange problem with it.

At first I couldn't get it to write DVDs. I tried everything (different software, aspi drivers, media, etc). It was only reading DVDs, but not writing. It wasn't writing even CDRs! I even restored the original software which came with my notebook (HP Pavillion ze4502). That didn't help.
But when I had reintalled Windows XP myself the drive began to write! (Crappy original configuration of HP?) But now it doesn't read DVDs properly, the picture freezes all the time. (It starts to read, recognizes DVD, but the picture is changing not smoothly).

It's strange, because I have another (internal) CD burner (which reads DVD also) on my notebook, and all the time it works properly, now and then. It reads DVDs fine.

So to make a long story short (or is it a short story long?) the problem is
it used to read, but failed to write. Now it writes fine, but reads poor. And I know it can and should, because it used to. What could cause this roblem?

I don't think its video adapter, because I installed all the drivers and it plays DVDs fine when they are ripped to hard drive or when I play them on my other CD/DVD drive.

Any ideas?