Why does my computer shut off when I play games?

When I first got my computer, I had absolutely no problem playing games. I can max out a lot of games, and I played perfectly for hours and hours. For about a week or two, my computer has been randomly shutting itself off about 10-20 minutes into the game (Such games as Crysis 3, GTA 4, EFLC, etc). I was thinking it may be something up with the computer having problems, and was thinking of reformatting to be able to play like it used to, but first I want to see if there's anything else I can do. Here are my specs:

Mobo - Gigabyte GA-990FXA-UD3 AM3+
CPU - AMD FX-8350
CPU Fan - Standard Fan Came With CPU
GPU - EVGA GTX 650 1GB
PSU - Corsair HX750
RAM - Corsair Vengeance 8gb (2 x 4GB)
Screen Resolution - 1280 x 1024

If anyone could give me some help into what may be causing my computer to shut off, please do help!

 

Could be heat, an issue with the PSU, or even the hard drive in rare cases.

Are you monitoring your temps?

Are they below 50 C?

 

I have not monitored temps, how could I reach the temperatures?

 

A couple of monitoring tools, for fan speeds, CPU and GPU temps http://www.majorgeeks.com/files/details/system_monitor_ii.html and http://www.majorgeeks.com/files/details/gpu_monitor.html . Any chance your case/fans are dirty and need blown out? Also, I suggest looking through this http://www.majorgeeks.com/content/page/how_to_make_your_computer_run_like_new_in_4_easy_steps.html . Good luck!

 

clean your Chassis fan，or change your computer for more and more games become killer of the old machines.