This is frustrating I have i-tunes on two PC's and on one everything plays fine but on the other 70% of tracks will not play as a box comes up saying I must authorize this computer so I do and then a box appears saying this computer is already authorized

I have a PC laptop with all my i-tunes library on and a desktop where I edit Photography from that has i-tunes as well. I can play all my tracks on PC laptop but when I try to use desktop only about 30% of tracks play? and a box appears saying this computer needs to be authorized which I do, then it says it is already authorized, so I try to play a track and another box comes up whith ? yes you've guessed it!!!! This computer needs to be authorized. This is driving me insane as there is no way of contacting any apple reps as they are so hellbent on no human contact HELP!!!