Why do you believe it is corrupted?

Officially there is no way to remove nor reinstall the player: it's part of
the OS, so any repair or reinstall would have to be done at the larger OS
level.

Will your WMP 11 on Vista play anything at all? If the WMP only has
problems with certain file types, you might need a codec download for
that file type. If you have other players such as Real or Winamp, try
to play a file that does not work on WMP 11 on the other players. Real
11, the most recent Winamp, and a few other players now play some
Windows format media files such as wma and wmv. The more details of
the problem you have that you can give, the more likely it is that
someone can help you find a solution.

Zachd, who answered you, likely can help if you provide enough
details, as he is associated with the WMP. It is true, as he stated,
that Microsoft considers the WMP 11, as on Vista, part of the OS and
thus officially you can not remove or replace it. However a version of
WMP 11, slightly different in details I am sure, can be installed on
the XP OS, and you can return to a previous version such as WMP 10,
alhough you can not completely remove WMP from the XP OS.

I have not kept up with the most recent events, but Microsoft has had
much trouble and stiff fines from the EU officials recently. They may
not be able to bundle the WMP with the OS for sales in the EU. If this
is so, you might be able to see if you can get an EU version of the
Vista OS or if someone knows how to remove WMP11 from the bundled WMP
11 and then add or remove the WMP of your choice to it. You would have
to find this out from someone in one of the EU countries, because I
highly doubt if Microsoft would be willing to provide any information
concerning this, if it has any, to those having Vista with a bundled
WMP 11 OS.

If worst comes to worst, you need not go without a media player. Real
11, Winamp, and other free players will play most or all of the
formats WMP will play.