Computer freezing, suspected gfx card. Please help!

Hi,

I am having problems with computer lock ups while playing a certain game (Blacklight: Retribution). I get two types of crashes and they can happen at any time while playing, from sitting in the main menu, to being in the middle of a fire fight.

First type of crash I get is a complete PC shut off as if I have pulled out the mains cable, after a couple of seconds the computer turns itself back on again.
Second type of crash I get is a complete PC freeze. No amount of key combinations can free it up and the only way out is to hold down the power button and hard reset my machine.

I originally thought it was a problem with the game as it only happened while playing and my PC has been fine with everything else I have done with it (including a host of other games) since I brought it.

My PC spec is the following:
Intel Core i7-2700k 3.5GHz processor (overclocked to 4.5GHz)
NVIDIA GeForce GTX 560Ti 1GB gfx card
16GB RAM (4x4GB)
60GB SSD
2TB HDD

I have done the following in search of a solution:
- Thoroughly cleaned the inside of my computer for dust
- Tested each stick of memory individually with a PC boot
- Ran Windows memory checker
- Checked for loose power connections
- Monitored CPU and gfx card temperatures
- Reinstalled Blacklight onto SSD
- Turned every setting in the game to low and disabled

All of the above have had no effect and the problem is still the same. I have noticed I get less complete PC shut offs and more freezes though.

I have been stumped with this for a while now and decided to run some stress tests and monitor my gfx cards performance today. The first time my gfx card hit 79 degrees and then shut off like I had pulled the mains cable out, this is the first time I had managed to replicate a crash out of game and led me to my gfx card being the main problem. I then ran the same test again and this time it shut off in the same way at 85 degrees. I have yet to replicate the PC freeze crash but am assuming the crashes are coming from the same problem. This also leads me to believe that overheating is not the issue as the cut offs temperatures are not consistent.
I also read about voltages affecting stability, so I checked them in my bios and they seemed normal (3.376, 5.120, 12.096).

I am at the limit of what I know when it comes to troubleshooting and although I think I have identified the particular component, I am still stumped when it comes to why or what I can do to fix it.

My PC is only 6 months old so even if I have a dodgy gfx card I should be able to get a replacement. I just need to prove there is a problem.

Any ideas or help are greatly appreciated, Thank you.