Gtx670 crashing

System: gigabyte gtx670, 3570k CPU, 16gb corsair vengeance ram, asus sabertooth mobo, seasonic 750 gold psu, 120 gb samsung ssd and 2.5 tb Seagate hdd, noctua nh d14 in a cooler master 690 case

My first build worked fine for a few weeks until I started to play arkham asylum and about 5 min into the cutscene opening, my fans all turned up to max and the screen went blank. After letting the machine cool down for a couple of min, it boots up fine but won't get past the opening of the game. I figure the problem is with the game and uninstall.
I have been running borderlands 2 on high settings for a couple of weeks with no issues at all and after installing precision x, I up the GPU clock from 1060 to 1100 and run heaven benchmarker at high settings. It gets a couple of minutes in and I get the same noisy crash, so I reset the card to stock and run again, it still crashes. I figure I have a GPU issue and decide not to mess with the settings again.
A couple of days later borderlands 2 crashes the same way an hour into a game and now won't recognise my save file.
Now my new install of Starcraft 2 crashes the exact same way, blank screen, fans all suddenly max out until I hold the power button for 5 sec and I am stuck knowing what to do.

All drivers are up to date for GPU, mobo etc. and when running GPU z or CPU z all my temps seem low.
Is there a way I can diagnose exactly what was happening prior to the crashes? I figure I have a GPU problem but don't know how to find out for sure or what to do about it now? I bought the GPU from scan in the uk but don't have the original box and live in Switzerland so sending it back would be a major hassle, especially seeing as I don't know for sure that it is causing the problem.
I suppose I could buy the same card locally and if everything works ok, send back the original if I am still able? But am hoping to be able to diagnose and fix with the help of some of the experts here.