My bad its a 6870, and yes I believe it is kapoot
I would have RMA's it, but thinking I only had a 1 yr warranty on it (should have checked I know) I tried replacing the thermal paste to try and improve the situation. Unfortunately it made no difference.
Guess I could still try...
I have never owned a GTX 660, but i don't think i'm wrong when i say it shouldn't be running at over 70c full load, never mind 76c at 80%, i suspect its case ventilation but there is not much you can do about that with a HTPC case
Anyway, yes do try, you have nothing to loose, altho they may charge you for postage.