MKV crash Reason unkown

[Sonevar]

I've been running MKV files with VLC with no problems for weeks now, today I opened and watched an MKV, I closed it near the end of the file (closing credits) as normal, I activated mIRC and worked with that application for a few minutes beginning an avi file download, I switched windows to open the next mkv in the series I was watching, vlc opened and displayed the file title and runtime on the status bar as usual but no video or audio, the audio and video menus were both empty. I closed the file nd tried the previous one I had just watched, same problem, I tried other MKVs from other sources I had previously watched, still same problem, I tried other formats, avi, mpeg, and mp4 ran without error as before. I tried rebooting, no change except windows now reported that vlc had crashed and shut it down each time I opened an mkv, I tried uninstalling/reinstalling vlc (deleted cache and settings too) no change, I system restored to 2 days ago, no change. I can't understand what happened there was no change to the operation of my computer from the time vlc played the file I had watched and the time it stoped working (I had and still have the most current version of vlc for windows) I tried installing a different player and the mkvs ran fine.

Windows Vista Home Premium 32-bit
Nvidia GeForce 7350 (current drivers installed 2.5 days ago)

[Sonevar]

I ran RegCure registry cleaner... It works again... go figure...

[Sonevar]

After Watching an mpeg this time it began to refuse playing MKVs, I ran the registry cleaner again and this time it failed to get mkvs working... I'm totally confused