itunes wont Transfer purchases

My itunes isn't syncing with my computer. I recently cleared my computer and saved all my music and apps in an external. when i rebooted my comp and reinstalled itunes, it didnt let me sync my music and purchases to my ipod. I have already authorized my computer and it still wont sync. when i plug in my ipod, it says "syncing ipod", but its only for a few seconds, and when i look at my ipod, no songs have been synced into it. When i click on transfer purchases from itouch, i get this message saying it can transfer my purchases because im not authorized to play them on this computer. But i already authorized and reauthorized my computer. SO basically my itouch isnt syncing and nothing is being transfered from both sides. Any suggestions would help.