Problem after downloading new garageband - it won't accept password!

MacBook Pro (early 2008) fully updated and running Yosemite. Just yesterday I began the update of Garageband. But had to close my laptop before it could fully load. Tried today to finish. It wants my password, but despite even going through changing my Apple ID password - it STILL will not accept this new PW, or any of the others I have used in the past!