I noticed a problem in VLC on XP the other day. While watching a music video, I starting getting sound but no video. I thought it was some sort of display problem, but then tried QuickTime and found I could watch the video in QuickTime. Just to see if it would help, I logged off and back on. Still giving the same problem. I didn't change any settings, so I thought it was a hardware problem. So I shutdown the box and turned it back. Same problem. Argh.
I then realized that it must be some issue with VLC itself, so I started digging through the Settings menu; specifically, Preferences. Looking in Preferences -> Audio with "Advanced options" checked, I saw that "Audio desynchronization compensation" had reset to -10000000! Woah! How did that happen? I reset this value to 0 (zero) and played back my original video. Voila! The video played perfectly.
I don't know what key combination or bug I may have triggered, but that is a wacky one. Hope this helps someone in similar distress.