PC just started Randomly freezing - Vista x64

My PC just started to randomly freeze starting last Saturday. and it does for no reason it seems. Ive had my PC for about 6 mouths and last Saturday is the first time it has frozen and now it has been doing it just about everyday at least once. Each time i have to do a hard restart and when it freezes my sidebar CPU monitor says that one of my cores is running at 100% every time. Does anyone know how i can fix this problem. Please help! Thanks

Intel core i7 920 @ 2.67GHz
ASUS P6T Deluxe V2 motherboard
6GB CORSAIR XMS3 - clocked to 1600MHz using BIOS/RAM software - voltage @ 1.65V
EVGA GeForce GTX 260 - drivers just updated
if you need more info about my PC or my problem just ask.

P.S. i am going to Run memtest86 tonight.
Also it likes to freeze for the smallest things like when i open a notepad file, or watching a movie, or streaming a show online, or today i clicked on a link.
Yet when i play MW2 for an hour online with everyone on high it works great and never freezes.