If you open your My Documents folder and then browse to My Music then open the folder marked iTunesIn there you should see a folder called iTunes Media, If you could open that so you then see all your media and music listedOnce you have that can you then open iTunes and when iTunes is open can you then place the iTunes media window over the top of the iTunes program and press COMMAND+A to select all yoru music and media files then drag them to the iTunes library window and drop them like this
Once that is done all your files should then be reindexed back into iTunes so they shoudl all show up and play correctly
If you would try that and let me know if you have any issues or need any clarification
Ok,so do all your files show up in the iTunes Media folder?If so can you go to iTunes and then press Command+A to select all the entire library then delete it so that iTunes is then empty.
Once the library is empty can you then repeat the stpes I originally posted and let me know if the library will then index correctly, If not we will need to clear out your com.apple.iTunes.plist file and then see if we can reindex your library again