wmp "files missing"

I have a brand new Dell Inspiron laptop 1521 w/ V. Home Premium. When I try
to play a DVD, a media center screen comes up telling me "files missing".
Other times, it will play, but clearly all is not right -- it's choppy and
barely in sync.

I would try re-installing WMP, but I can't find a Vista version on the MS
site, nor can I figure out how to uninstall the current version (it's not in
the Program uninstall list).

Any help or guidance would be gratefully appreciated.