Please help. PC shuts down.

[Zessu]

Last week i changed my old HD 5770 to Gainward gtx 660 ti phantom and whenever i play borderlands 2 after hour my screen goes all red or black and then pc restarts. Also my screen goes black from time ti time while playing Guild Wars 2. At first i thought that it was PSU, but it has enough power to keep card running. Restarting does not happen with games like WoW, LoL, Torchlight.
So I am looking for advice
My PC:
core i5 750 not oc
gainward gtx 660 ti phantom.
Fortron raider 650W PSU
4 gigs of ram

 

[johnb35]

Most likely bad video card or bad drivers. Have you installed the latest drivers from Nvidia? What operating system are you running? 32 or 64bit?