PC Freezes after boot

My pc, almost a year old now is acting up. Everytime I start it up, it freezes. Its not instant, but as soon as W7 is loaded it will freeze in about 2 minutes. So I cannot even run any programs to test it. I really have no clue what to do. I just recently got the mobo replaced, and it was working fine right up until yesterday. I tried some troubleshooting but Asus isn't very helpful. I was told to do a clean install, which I did, but ever since it still is acting up, making me think its a hardware problem. I ran memtest86 last night, and it passed the tests 9/9 time. PLEASE HELP.

Western Digital Caviar Green WD7500AADS 750GB
Cooler Master V8 RR-UV8-XBU1-GP
XFX Black Edition P1-750B-CAG9
Sapphire Vapor-X Radeon HD 5850
Asus M4A88TD-V Ebo/USB3
G.Skill F3-12800CL7D-4GBRM
AMD 1090T

 

I hope that's what it is. I will try that here in a little bit when I get off of work and let you all know.