What do you mean by that? Do you mean videos you set to play when you put the computer in standby don't automatically resume? That's normal, and caused by google's timeout system (part of their content protection system)
If you mean that no videos will play after you resume from standby, including newly opened windows, that points to a graphics driver failure and you should reinstall your drivers
If you mean that the videos don't auto-play but they load, try pressing pause and then play again. If that works, it's just a bug with youtube, happens all the time.