Disassociating from an old Apple ID I recently change my Apple ID and password. However, now I an unable to use System Preference; each time I click on System Preference I am asked to input password for the old Apple ID which doesn't exist any longer. How can I disassociate my MacBook Pro from this old Apple ID which doesn't exist?
You didn't erase the old Apple ID, it still exists. Not using it doesn't make it go away.

All the apps installed on your machine, including the OS itself, are tied to that original ID.

The only way to be rid of it is to reformat the boot drive &amp; start over; install a fresh OS, repurchase all App Store apps under the new ID.

The essential paradigm difference between Apple &amp; Microsoft is that Microsoft ties a purchase to a machine.
Apple ties it to a user.
This makes changing machines easy, but changing users difficult.