I recently updated my nvidia drivers for my 6600gt card from nvidia's website. After doing so, whenever I try to open a video file with any program (VLC media player, Windows media player, Quicktime) the file does not open and performance on the computer grinds to a  halt.  
 
Has anyone else experienced this problem and know of a solution?
I'm running windows xp pro and have the latest versions of all my media players as well. Interestingly, when I run itunes for music I don't have any performance issues or hangups. Also - streaming video on youtube or google video works fine.

Try uninstalling the new drivers and reinstall the old ones to see if the problem disappears.  If so it could be a driver problem.  New drivers arent always the best ones.  If your not haveing performance issues and the new drivers dont increase performance or correct a problem you were haveing then there really is no need to update.

 
I tried this, yet everything still locks up when I try to open a video file. It doesn't matter what program I try to open them with (VLC, windows media, quicktime) they all crash and the computer freezes when I open a video.
 
I've run virus scans and antispyware; there doesn't appear to be anything malicious on my computer.

hi.
which player is your default??
maby your installation has changed it.
try to right click the video file ( open with )and specifie the media player.
i use vlc for every type of media.

clean up all your codecs and start from scratch
also test your directx to make sure it's not messing up with dxdiag.exe

I updated my bios and soundcard drivers and that fixed it. Go figure.