WMP video playback issue

I have WMP 11 and I'm trying to play an AVI file with an Xvid codec. For some
reason, it doesn't play; it just stays at 00:00:00. I can move the cursor and
see each frame fine, but, if i press play, nothing happens (apart from the
icon changing from 'playing' to 'paused'. It uses an independent subtitle
file (.sub) and DirectVobSub, if that's of any relevance. When doing this on
a computer with XP, it worked fine, but for some reason not on this
particular one, which is Vista.

ADD: It works perfectly when opened with PowerDVD.

Scratch that, it plays in x2 speed in PowerDVD and whenever I put it back to
x1, it pauses and reverts back to x2 when I press play.