The system check fixed a file called secpol.msc, but it doesn't seem to be related to this in any way.
The media player works fine. I'd just like to get it back to use the default codecs as Oblivion doesn't seem to like non-default codecs. I do not have Nero or it's codecs installed. I only had the Vista Codec Pack from this forum installed.
Also, as the title indicates, I could not find a way to reinstall or repair WMP 11. That's why I created this thread to get help on that one.
Thanks for the answer.