Troubleshooting New System Lockup During Gaming

Hey guys, I recently built myself a new system (for the first time).

Asus P5E WS Professional X38 socket 775
Sapphire Radeon HD 4870
Mushkin HP2 6400 4GB (2x2GB) DDR2 800 5-4-4-12 (1.8V) 240pins (996587)
Power and Cooling Silencer 750 Quad Crossfire 750W
Vista 64-bit home professional
Antec Nine Hundred Black
etc..

Everything works fine, however my games seem to keep freezing and locking up randomly during play (some games more then others but the lockups weren't that frequent, just once in a while). At first I thought it was a definate RAM issue so I posted for help in the Mushkin Forums and they suggested tweaking my RAM settings in the BIOS. When I play Spore I noticed that when I went into the system setting panel and tweaked the RAM usage number my system would lock up and after I tweaked my RAM settings in BIOS (as suggested by the Mushkin folk) my system stopped locking up in Spore which was promising. But now it's locking up when I play Sims 2 (just installed recently) and Warhammer Online, so I'm starting to get frustrated.. (it's worth it to note at this point that when I play Crysis I have no problems what-so-ever... never had a Crysis crash as of this date, kind of odd) This is how my screen looks during crash..


Basically my sound locks up, I see blocky squares twitching and I have to force a reboot....

Can anyone offer some words of advice? How can I figure out once and for all what the problem is?

I would try first running it with case open and a fan on it just to see if you have an airflow / heating problem. Second, patch everything - bios, motherboard drivers, sound , video card.

Next run prime95 for a few hours, to isolate it to cpu memory, or something else like vid card. If you can isolate then you can tweak settings, underclock it etc....

Good luck.