authorize

i have had this account for a really long time and my work gave me an i phone 4 and work station for promotion and due to a few fresh start wipes on my home pc it says i have reached my limit of five authorized pc on my account which is not true i only have two pc's at home but this bieng to third time i have clean wiped and reinstalled windows due to new hardware and what not. i wont be able to authorize my workstation at work. is is there a way to deauthorize itune post wipe?