Help with a CPU Problem

Hello there, I have a problem with a CPU I recently purchased. I installed the CPU fine, and it runs fine, but sometimes the PC randomly freezes, the monitor losses signal, but I can still hear the fans running, and the PC is in fact still working, though I can't perform anything other than hard reset to get the PC up and running again. I've checked the Windows Event Log, and there are no errors during the time this happens.

I have a MS-7329 motherboard (Intel P31 Neo V2 Chipset), and the CPU I bought is Intel Core 2 Duo E7500 2.93 Ghz, and the CPU I had before that one was E2200 2.2 Ghz. I also recently purchased a new PSU unit with 550W. The reason I know that it's the CPU problem is because if I put my old CPU back it runs fine. I've checked the temperatures in BIOS, and the CPU temp was 50 C or 51 C (system temperature 37 C), while using Real Temp software it says 37 C on both cores, in idle mode. And under 100 % load (checked with Intel Burn In Test for about 5 minutes) it never goes more than 80C. When I'm gaming, the temperatures always stay below 60 C.

My question is: Is there anything else I have to adjust when replacing the CPU. I did everything by the book: removed the old heatsink and the fan, removed the old CPU, placed in the new one, added thermal compund, and placed the new heatsink on it. The first time I installed the new CPU this problem was very frequent, then I tried reinstalling it again, and this time the CPU worked fine for 5 days, and then the problem appeared again when I'm watching videos or gaming.
Could I have damaged the CPU? Or might there be something wrong with my motherboard? Do I have to flash my BIOS perhaps?

My full PC specs are:

Intel Core 2 Duo E7500 2.93 Ghz
ATI Radeon 4850 HD 1 GB GDDR5
MSI - 7329 (Intel Chipset P31 Neo V2)
MicroStar 550W PSU
4GB DDR2 800 Mghz Ram Memory

Any help would be greatly appreciated. Thank you.