Songs in My Music not appearing in itunes--Help, help

I have quite a few items in My Music file that do not appear in itunes. I am moving to an ext. hd & would like to fix this before I do the move. Also, should I back up to the ehd before I do the move or are they the same thing?

I am having the .dll issue & plan to uninstall/reinstall after I have moved my folders over.

Thanks for you patience & help. I am a nervous Nelly!!