System Locking Up : I'm Stumped

I built a new computer in March of this year. About three weeks ago it started locking up, and I had to hit the reset switch on the box (CTRL+ALT+DEL doesn’t work).

I ran Memtest, and it gave me a bunch of Memory errors, so I took the faulty memory back, got new memory and put it in. It’s still locking up.

I ran memtest for 6 hours last night and no errors were reported. I formatted my harddrive, turned off ALL overclocking, reinstalled drivers and games and cannot determine what the problem could be. Here is my system:

Q6600 @ 2.4ghz
XFX 780i MB
Patriot pc8500 Memory (4gb)
eVGA Geforce 9800 GX2
Maxtor 400Gb Harddrive (hooked up via SATA)
Vista Home Premium x64

I mostly have this problem when playing games, LOTRO and Age of Conan. I don’t know if it could be a faulty motherboard or video card, or if the harddrive itsself is having problems. Suggestions?

Nice spec!

What are the cpu/gpu temps like?

What power supply do you have?

BAD video card…