Vista - Media Player Library

So ive been using Vista, with its Media Player 11 for months now.

Mplayer was working great, but this week it now does not recognise any music
on my computer.

Each tme you open mplayer, there are no files present, you click library, no
files have been added. You click the tab/file menu to add a library, which
does not do anything.

I though this could be due to a recent program installation, so I ran
windows restore point to when I knew it worked fine - but nothing!

Any suggestions??