Fullscreen Flash Video Completely Locking Up PC?

when watching Internet videos in fullscreen, eventually the screen turns purple and becomes pixelated. the sound of the video continues for a few seconds, and then even that stops. i can't alt tab, escape, use the windows key, and not even ctrl alt delete will do anything. my only option seems to be to restart. i've managed to reproduce this around 3 times today alone (the error doesn't happen instantly upon going fullscreen into the video, and it doesn't happen at all if i don't do fullscreen).

i want to note that i'm still using a hard drive that's been considered bad by a number of diagnostics programs since early february, but since this is a repeatable scenario related to watching videos on Internet, i want to assume for now that that isn't the main cause (because i don't want to replace the drive right now if not absolutely necessary).

notable things are that i've recently replaced my gts 450 with a 560 ti, which seems to be fine. i play bf3 on ultra, and temps only go up to about 67c (i'm playing on 1440x900), so i don't think this is a problem with the card. maxing gtaiv works fine as well. the only other thing is that i updated my drivers to 296.10 yesterday. is this likely to be the cause of my problem, or is this a possible symptom of a dying hard drive?