Need help PC crashing.

Robomoo

Honorable
Jun 13, 2013
29
0
10,530
This is my build:
http://pcpartpicker.com/user/Robomoo/saved/
I got all of these components new a few months ago except for the video card which is from an old machine and about a year old. Earlier today while playing team fortress 2 (a not particularly stressful program which this machine can usually run absolutely fine) the screen went black and everything just turned off entirely. This has only happened once or twice before as very isolated incidents and only ever during gaming- normally I turn it off for a few minutes and it's fine again. Today though it is crashing without fail within a few minutes of me turning it on.

My first thought was that maybe the fans had become too clogged with dust and it was overheating but even after carefully dusting inside the case and checking the core temperature (it seems to fluctuate around a steady 80-85C) I am having the same problem. Now I'm most worried that the problem is my (moderately expensive) PSU as a similar sort of situation occurred with a really shitty old one I once used- this ended with me flicking the wattage switch to see what would happen and the thing completely frying. But to be honest I really have no idea exactly what is going on with it, which is why i'm posting.
Any advice?