I dunno, mine seems to be okay now..
I've set the fan speed manually to 70% and the temps
on my GPU never went over 55 during Crysis..
Got to max 50 on the CPU during Crysis but it was IDLING at 70 before
so, that's a huge improvement
I couldn't even play for a minute before the system shut down but
I just finished playing for 30 minutes straight without a hitch..
I'm pretty sure your card isn't faulty.... if you've tried a new PSU, and your CPU isn't overheating
it must be the 280 overheating when you launch a 3d application..
it shuts itself down to avoid damaging itself..