Have you had a chance to do the trouble shooting steps I suggested. Swap Cards and see if the problem goes away.. If it does then its the card!! etc..
Problem like that would drive me batty.. I had a similar problem on a old rig I built back in Jan.2002
ABIT KR7A:
AMD-1900 XP
PC-2400 Corsair
etc..
This was one hell of a gaming rig. I had one problem, it kept crashing. It would do it while playing, while idling. I reformatted numerous times, tried different GC's. Nothing worked. I was getting plenty pissed. I ended up selling for 500bucks and purchased my Current Big Blue Rig!! The guy who bought it figured out that the Mobo only supported PC-2100 Ram. He had some and said it ran stable as hell.. I read all the manuals and specs but I was reading the New Ones based on Version 2 of that MOBO. I had Version 1 which only supported 2100.
Live and Learn.. I didn't try swapping out the RAM but I tested it at a nearby shop and it was good.
Where was I going with this...... Oh Troubleshoot to find the cause.. Odds are its the GC, PS or Ram..