Asus P8B75M-LX crashing with GTX 660Ti

Hello,

Here are my original PC specs:

i7-3770K 3.4GHz (Turboboost up to 3.9GHz)
ASUS P8B75M-LX motherboard
8gb DDR3 RAM
4GB ASUS GT630
700W PSU

I decided to upgrade my GPU to an ASUS GTX660Ti as I the GT630 was crap. However upon installing and running the GTX 660Ti on maximum settings for GW2 or Metro 2033, the game crashes after 5 minutes and the PC would reboot itself. It also crashes when I run a Heaven 3.0 benchmark test (direct X9 default). I borrowed a friend's Radeon 7950 and it runs smoothly on my PC for GW2, Metro and Heaven benchmark test. My friend could also run my GTX660Ti smoothly on his PC with no trouble. The only drawback with GTX660Ti is the lower memory bandwidth.

Now, my question: Is it worth returning the 660Ti and getting a GTX670? Or should I send my PC back to the manufacturer and test the motherboard/PSU?

Note: When running at highest graphic settings, the GTX660Ti definitely performs smoother than the 7950 (for GW2 at least). I am worried that if I get GTX670 and it still crashes, then it could be a motherboard/PSU problem (but shouldn't that be the case for the 7950 also?).

Would appreciate some feedback. Thanks.