Hi, Lotvic, It's been doing this for about two weeks, WMP doesn't seem to like anything, VLC does it quite a lot, so does KM Player. It's also a problem within Picasa. Haven't installed anything new lately - as I recall......
I'm not on XP at the mo but check that DEP is only selected to Windows features and not others. Otherwise try system restore to before the problem. Might be something you installed as Lotvic suggested.
Yes there are some strange results in google. Have a look in Device Manager and see if there are any warning triangles, it might be a driver.
I'll keep searching, if they won't even play in VLC something's gone wrong.
Have you tried updating Adobe Flash, WMediaPlayer and VLC?
You could always try sfc /scannow to troubleshoot missing or corrupted system files (system file checker) to troubleshoot missing or corrupted system files, you might need your xp CD if it asks for it.
Start, Run, sfc /scannow (note the space after c and before /)