PC goes into sleep mode while playing games for my AMD 7750

[amd7750]

Hello guy's. I need urgent help. When i play games like BATTLEFIELD 3,NFS HOT PURSUIT". My screen turns black and pc falling sleep.My screen goes into power saving mode.This never happens when I am browsing the internet,watching movies.I have to restart to get the signal,i cant do anything.I also have tried by changing the windows power setting.

MY specs are:
Operating System: Windows 7 Ultimate 64-bit
Memory: 4 GB DDR3(transcend)
Processor: Intel(R) Core(TM) i5-3470 CPU @ 3.20GHz (4 CPUs)
Motherboard:Gigabyte B75-d3h
Graphics card: SAPPHIRE AMD 7750
PSU: Corsair vs450

NEED URGENT HELP

 

[amd7750]

MAY BE I NEED CPU AS WELL AS GPU COOLING PASTE ,DONT YOU THINK SO REPLY ME PLEASE

 

[Onus]

If the fan made no difference, then I misread your post. Since memtest found errors, that's where I'd focus then. Replace the defective RAM if you can't get what you have stable with looser timings or a tiny voltage bump.

 

[amd7750]

HEY I TRIED DIFFERENT RAMS IN DIFFERENT SLOT ,IT DID NOT MAKE ANY DIFFERENCE ,MAYBE MY GFX CARD IS FAULTY BECAUSE I HAVE JUST UPDATED MY MOTHERBOARD FORM GIGABYTE GA-G41 COMBO TO GIGABYTE GA-B75 D3H COUPLE OF MONTHS AGO AND ALSO CHANGED POWER SUPPLY TO GET RID OF THIS IT DIDNOT MAKE ANY DIFFERENCE SO I THINK MY GFX CARD IS FAULTY

 

[Onus]

Please do not post in all caps. Thanks.
If every other part in your system has been changed, and additional cooling is not helping your graphics card, then it probably is defective. Contact Sapphire about warranty replacement.