Desktop freezing but everything else works...

Hey this is my first forum post, I'm new to this. I just built my first gaming rig and have had everything working for about a month. The other day i downloaded some windows updates and downloaded that free microsoft anti virus security essentials. Since then whenever I leave my computer alone on the desktop for to long on idle it freezes but no blue screens. It even does it when I'm downloading something. What's weird is I can run everything else without any problems except this. I uninstalled the anti virus and saw a performance boost but it didn't fix my problem. I even checked my power management setting and no go. If anyone can help me i would really appreciate it because I feel like this is a stupid problem for my computer to be having and it's killing me that I haven't figured it out. Another thing I forgot to say is when I put the computer to sleep it works but then when I hit the power button to come back it turns on but my monitor doesn't acknowledge its back on. Then i power it down and restart it and then the computer comes back from sleep like it should but I don't know why this is also happening. I was just wondering if its connected.
My specs are: intel core i7 2600k 3.4GHz
ocz vertex 3 60 gb ssd for OS
asus sabertooth p67 rev.3
8gb pny 1333mhz ram
2x MSI twin frozr 3 6950's in crossfire
wd caviar black 1tb drive for storage
coolermaster silent pro gold 1200w
windows 7 64 bit home premium oem

Thank you everybody!