....when you switch to full screen.

I can play anything else, normal movies in WMP/VLC etc. full screen with no bother, but on any site that plays Flash videos (Youtube, Vimeo etc) the screen freezes when you try to play full screen.

WTF?

 

Don't know but I've had youtube etc try and make IE download a new version of flash player the last few days?

 

Sounds like a flash player problem.

Maybe try uninstalling flash and downloading the lastest one.

Or alternately you could try another web browser and see if the same happens, if you dont have two different ones installed then the first option will be easier.