HT1420: Authorize or deauthorize your Mac or PCLearn about Authorize or deauthorize your Mac or PC
Currently Being ModeratedNov 14, 2012 11:03 PM (in response to ginbo88)
Your account is authorised on your computer's iTunes (Store > Authorise This Computer menu option), and do they not copy over via File > Transfer Purchases ?
There are also a couple of user tips that might be of help :
https://discussions.apple.com/docs/DOC-3991 - recovering content from a device
https://discussions.apple.com/docs/DOC-3141 - syncing to a new computer (which you effectively are doing if you've re-installed the OS)