Computer freezes while playing Games!

[i1stProdigy]

Hi i'm new here so, excuse me if i posted this in the wrong section. 

I have been having a problem with my newly built PC whenever I play any steam game and even League of Legends after about 20-30 minutes of gameplay or sometimes less my entire computer freezes and I get a black or white screen and a even a dark green screen with lines all over and i can't see anything nor do anything I have to manually turn it off by holding the power button, I'm guessing its either my graphics or power supply but I don't know... any help?

 

PC SPECS- OS: Windows 7 Ultimate 64-bit

                   CPU: AMD FX-8350

                   MB: Asus M5A99FX PRO R2.0 

                   GPU: XFX r9 280x Double D

                   RAM: 2x 4Gb vengeance DDR3 

                   PSU: Corsair CX 750

                   HDD: 1TB western Digital

                   Cpu Fan: Noctua nh-u14s

                   Case: Corsair Carbide series 300R Mid-Tower (Black)

 

P.S: I'm not overclocked

[Clyne]

Try disabling AMD Turbocore and downvolt.......worked for me on my 8320 with crashes.

[i1stProdigy]

Ok not to sound like a newbie cause i do have some knowledge on pc stuff but...how do I disable the AMD Turbocore and downvolt? 

-I went into bios but dont see anything on it please help.

[i1stProdigy]