If you still have not resolved this problem here is something else to try.

I had a power outage on one of my systems a couple weeks ago and when it rebooted whenever I tried to play any video file avi, mov, wma, on any video player wmp, quicktime, nero showtime, all I got was audio and no video.

I got all the usual suggestions - check to see the proper codecs where installed, reinstall the players, etc. and nothing worked.

I was about to throw the computer through the wall or re-enact the scene from southpark where the general calls Bill Gates on the stage after w98 locks up and shoots him in the head!

As a last resort I completely uninstalled my video drivers (nvidia) and re-installed them and viola all the video formats started working again.

Oddly enough just yesterday we had a power outage and a different machine I own started doing the same thing. It would play audio but no video. Of course I forgot what I did to fix it on the other machine by this time and spent the day going through the same ritual of checking all the codecs, reinstalling all the players, rattling voodoo beads over the computer and sacrificing a live chicken, considering hiring a witch doctor to place a curse on Bill Gates and then I remembered to uninstall and reinstall the video drivers and the problem was again resolved.