It's really weird because fullscreen videos worked perfectly fine until yesterday morning.
Googling "youtube won't play fullscreen videos" just gets me advice for what to do if the screen is completely black (or white) which isn't the problem I have. (I did try that advice anyway--which was basically to uncheck the hardware acceleration box in Settings after right-clicking the video--and it didn't help) Also tried doing a CClean and that didn't help either. I can't think of what else I should try for this.
Using Google Chrome on Windows Vista, HP Pavilion dv6000 laptop.