Do you have any stability problems aside from youtube videos? Does your system freeze or artifact when playing games? If this is just youtube it's possible that you are having flash issues. Try uninstalling and reinstalling flash. You can try disabling SLI or removing one of your video cards, that may be an issue. Finally, try rolling back to an earlier driver revision, it could be the latest nvidia drivers don't interact with flash video properly.
There are no other stability problems. Game doesn't freeze or artifact. Not yet anyway. Prime95 ran for 12 hours without errors. FurMark ran for 20 minutes without artifacts. It's hard to reproduce this problem because it doesn't always happen. I will try your suggestions.
I have the same problem, it have happend to me 4-5 times now. what i notice is the simlarity on our computers is the graphics card (I have 1 Gainward GeForce 560 TI Physx) and it started happening after the latest driver update to the nividia drivers. I think maybe the problems are there.
Go into your Nvidia control panel and change your power management mode to Prefer maximum performance, some people have trouble with freezing etc when browsing or on youtube when it is set to adaptive...hope this works for you.