Hey T, Sounds like a codec's prob. See Links below.
Have a look at the thread below for links to heaps of codec packs (some people like the XP codec pack for WMP & the K-lite pack's popular too).
CODECs list for Movies/Alternate players / Video help forums/ video-mp3 fixers
That thread also has a link to VLC player. It's free, has codecs installed & is very reliable.
And here's a link for Vista codecs, just in case you're using Vista.
Vista Codec Package v4.4.8 (freeware).
Hope this helps.
