Uninstall LW as a last resort. Try the other things first. Do not use the add/remove control panel to uninstall LW. Go to Start menu -> Programs -> LW -> Uninstall.
If you don't uninstall it correctly you will have major problems.

As for the song you lost .. I am not sure. iTunes has been a bit buggy in recent versions. Try searching your computer for it. It might still be there somewhere. If yes, re-add it to iTunes using these techniques: How to transfer music to my iPod (& iTunes)