Computer restarts unexpectedly when playing games

[hmdfrs]

I just build this computer 2 days ago, all items are new.

Here's my spec;
Intel Core i5-4460
Gigabyte H97-HD3 Motherboard
Cooler Master Power Supply Elite V2 550W
Sapphire DUAL-X R7 265
Vengeance 4GB Ram x2

The restarts happen after an hour or two in game. Sometimes less than half an hour.
Monitored my system heat (cpu and gpu), no significant heat change stays, only around 55 degrees C ( in game ) and 40 C.
Updated BIOS but it still happens.

Any chances of solving this without having to change any hardware?

 

[Tmagic650]

The Sapphire DUAL-X R7 265 may need its thermal paste replaced. How old is this video card?

 

[hmdfrs]

The Sapphire DUAL-X R7 265 may need its thermal paste replaced. How old is this video card?

New I guess? Unboxed it myself. I'll try replacing the thermal paste.

 

[Tmagic650]

Well, if it is new you may not need to replace the thermal paste. Can you return it under warranty?

 

[hmdfrs]

Well, if it is new you may not need to replace the thermal paste. Can you return it under warranty?

I don't think I can return it. Let's rule that option out if can.

(btw, still didnt replace thermal paste)
The auto restart happens again. This time, on booting the pc (2 times) and windows update (once). I'm not even in game.
Does this means the GPU is not the problem?

 

[hmdfrs]

Monitored the hardware using MSI afterburner.
This is what I get when playing game until it crashed.

 

[Tmagic650]

Can't read the file

 

[hmdfrs]

Can't read the file

use RivaTuner

 

[Tmagic650]

No thanks...

 

[hmdfrs]

I think I need to change my PSU....

 

[Tmagic650]

Sounds like a good thing to try