Resetting Apple ID

I migrated info from on computer to another, including iTunes info. Now, my new computer isn't "authorized" to play some of the songs I've purchased (I can't find rhyme or reason as to which can and can't be played, although it may seem that it is older songs that don't work.)

I think the problem may be that my apple ID refuses to reset to my current one - it keeps reverting to an old AOL email addy I had years ago. Is there a way to go in and change in manually so it stops popping up? I keep going through the steps to "authorize" the computer, and it says it's successful, but then the window shows up again (with the old Apple ID in it) saying I need to authorize i.