So I built this computer back in August of 2012 and it ran great with a Nvidia GTX 560 SE but around X-mas I decided to replace that with a GTX 660 listed above and that ran good playing various games for a bit but the first time I booted up Skyrim played for a while and then my computer just restarted. This freaked me out so I booted Skyrim up again to see if that was a one time thing and played for a good few hours and it never shut down.
I thought this was very odd and payed it no mind till It happened the following night and so on after that It would sometimes work fine, sometimes restart my PC within 5 minutes. I also get reboots messing around in the UDK just loading an example level or reboots in other Unreal Engine games like batman arkham city.
This doesn't happen in all games for example I can play Dishonored, FFXIV Reborn, Shogun 2 Total war, and many other games fine.
So what have I done to try and fix it? Well I check all my temps and those are all fine (CPU around 50 - 60 under load and GPU around 65 - 75 under load), no overclocking has been done not even to ram its all default. I turned off CPU turbo mode in my bios and ran memcheck with no errors after 3 passes. None of this worked on its own.
So last night I switched out my GTX 660 for my 560 SE and no restarts! So my question in the end is, would it be more likely that my graphics card is having problems or that my PSU maybe can't support the 660 as it is more power hungry or causing voltage spikes? Or is there something I am total missing?
Sorry for the wall of text or if this is in the wrong forum (first time poster!) thanks a bunch for the read/help if you have any.
P.S Let me know if I am missing some spec that is very crucial!