That sucks. Have you tried Files/Add to Library and just pointing to the folder where all your music is? Its a brute force approach but should at least get them in.
If it still doesn't work, try renaming the file "iTunes Library" to "iTunes Libarary Old" and next time you open iTunes, it will regenerate it. You will lose all your ratings, but if that file is badly corrupted you may have no choice unless you have a backup of it you could try? There's also a file called com.apple.iTunes.plist file you could delete and see if that helps. Its the iTunes preference file, and you will find it in the Preferences folder of your home folders Library.