Disappointed Angel

My windows media player 11 used to work perfectly (in Windows Vista Home
Premium) but now it does not work, I don't know why. I believe it can be
related with 'network sharing' because one day it appeared an error message
saying something about network sharing and that it was going to be closed.
From then on wmp library has never worked again. I tried to add files by
myself, but once again it didn't work. I can play music and videos without
any problem, but those are never added to the library. Windows Media Center
library does not work either and I don't know how to solve this problem.

I would be more than glad if anyone could give me any solution.

Thanks