Please

I've just updated my iTunes and it says i have 22920 songs but quite a few of them have a ! (explanation symbol) next to the track name in a seperate column.

Any ideas what that means?

I've also managed to import some songs from my mates iTunes but its saying when i try to play them that it cannot find the original file even tho i have them as Mp4's on my hard drive

Also is there a way of deleting the songs that i have 2, 3, 4 etc.... copies of? i.e. duplicate songs?