I know from my own personal experience, I have a GTX 750 Ti that was getting very small white/black splotches when hardware accelerated decoding of videos. I ended up opening up the shroud, dusting it out thoroughly, and reapplying some thermal compound. So, I wouldn't presume it's dying necessarily, but it may need cleaned. But like TotalInsanity4 says, you could look at the driver version and revert it first to see if that helps.