P5Q3 (NOT Deluxe or Pro) lockups

[quaestor]

Specs are in sig. Problem as in topic.

 

The reason I'm SO frustrated is that *everything* works, except for the completely random lockups and slightly more rare blackscreen/reboot.

 

I can get it lock up pretty reliably when using Handbrake to encode from a DVD, but even then it's completely random as to when (usually within 20 minutes).

 

It has also locked up when I open TextEdit on a completely quiet system that's sat idle for a couple hours.

 

GeekBench has never caused a lockup, even with multiple runs.

 

MPlayer will usually cause a lockup, but again, quite at random, within 10 min or so.

 

The system has sat idle (running OpenGL screensaver only) for 12 hours numerous times.

 

The system has slept for 12 hours or more and woken up no problem numerous times.

 

System has never locked up when hotplugging USB devices.

 

Large network transfers don't cause problems (copied Leopard Retail dmg from XP system).

 

Large dmg mounts don't cause a problem (can mount Leopard Retail dmg).

 

HELP!