What version of WMP are you using?
You can upgrade to v10 by visiting Microsoft website, and downloading the file.
If all you want to do is clear the library then this is easy.
Find your "Documents & Settings" folder,open it and there should be a folder with your Login Name, open this, goto "Local Settings">Application Data>Microsoft>Media Player.
There you should find one or more files named Cuurent Database ****. Delete these,and you will clear all tge file entries from the library, but still leave the music files on the hard disc.
You can then start from scratch and search for the music files you wish to re-enter into the library.
I currently have some 30 gigs and some 2000 music files on my PC and have no problems with WMP10.
Hope this helps, Toxin