I still think it's RAM. Ask someone to borrow you some just to see if you can boot.
Oh, I almost forgot. NOD32 ftw.
+1 for NOD32.
Oh, and to everyone saying it's his RAM/Hardware problem....it's not. OBVIOUSLY this all started after the OP installed AVG. Logic would dictate that this would be the root of their problem, and should be the first place to look....NOT the hardware. AVG is just about the crappiest AV program out there, and causes multiple problems depending on the system.