My computer plays sound for everything but internet videos

This may be a complete hurr derp moment and I feel really dumb for having to ask about this, but...I cannot for the life of me to get youtube videos and other flash-type videos on the internet to play with sound.

I've been able to watch youtube videos with sound up until last night. The only major changes I've made to my computer before that were that I recently downloaded Tor and I installed the most recent DivX player. I installed Tor on my laptop on the same day, though, and I can still watch youtube videos with sound there, so could it be the DivX? This happens in all of my browsers: IE, Firefox, and Chrome.

I have already...
1) Uninstalled and reinstalled Flash, Java, and Shockwave
2) Uninstalled DivX
3) Checked to make sure my video and audio drivers are up to date.
4) Checked to make sure the sound is turned up on the speakers, Windows, and the youtube video screen (see, I'm not completely derp!)

What am I doing wrong, oh techno-masters of the interwebz?

 

UPDATE: Fixed it. System restore took care of it. I still have no idea what caused the problem, but it's gone now.