Galaxy Gtx660 2GB Problem!

So my friend got me this GPU for christmas and it turns out the drivers keep crashing and mess up my gameplay. Basically, when i'm playing any game, after about 10 to 15 minutes into the game it goes all rainbow screen then goes black. After a few seconds, either the desktop shows up, the game continues as it normally would, or it crashes and i have to restart the pc. It really is a nuisance and i would like to fix it if possible. I was thinking the default clock speeds may have been too high for their own good so i want to try and underclock it a bit, but i have little to no experience in over/underclocking. Anyone here care to share a few words of advice?

 

My Specs:

Cpu: Amd FX 6300

Gpu: Galaxy GTX660

Mobo: MSI 990FXA-GD80V2

Ram: Patriot Intel Extreme Master 16gb(2x8gb)

Storage:120gb samsung 840 ssd, seagate 320gb 7200rpm hdd

Psu: Lepa 550w Bronze certified

Make sure you have the latest drivers and if that doesn't work you could try to disable the boost or set to stock speeds found on nvidias website 

After a while i decided that my case has too little ventilation and i underclocked it a bit and its running perfectly fine.