purchases on iPod not transferring to iTunes - "this computer not authorized"

25 items purchased on old PC, under iTunes account which apparently has disappeared - any way to recover?? When I click "Transfer", it says "some purchases on iPod not transferred because you are not authorized on this computer." The Mac used now IS authorized for the newer iTunes account, Apple cannot find record of older iTunes account so of course cannot authorize this computer for the older account purchases were made under. Ideas??