Apple installed a new logic board and now iTunes music is all gone and I cannot log into store or authorize my Mac

Question

I have an early  2011 i7 MacBook Pro running OSX 10.9.4. Earlier this week I had Geniuses at the Apple Store install a new logic board to replace a failed one. My hard drive was not touched. Anyway, when I got home and launched iTunes, I discovered that none of the tens of thousands of legally purchased songs in my iTunes library were listed, even though they actually still exist in my Music folder. Additionally, my attempts to login to the iTunes Store with my valid and correct and accurate and current Apple ID with the correct password, did not work. In fact,  no errors were generated. The logins simply erased my input after clicking SIGN IN and then the "Sign In" form came back empty.
As a developer and 28+ year user of the Mac, I was a little stunned to say the least. The Apple Store logic board replacement process should take into account iTunes authentication problems when replacing failed logic boards, but this issue was not discussed at all, in any form during the repair intake process. So, I now have a 'fixed' MacBook Pro that will not acknowledge my thousands of legally purchased songs and will not let me log into the iTunes Store with my valid credentials or authorize or de-authorize my Mac.
Indeed, iTunes Match is also disabled, which means $30 thrown away in paid subscription.
Does anyone know a workaround to this Apple flaw that can correct their mistake and re-enable my Mac for using my thousands of legally purchased songs?
Any feedback would be most appreciated!
Thanks,
Larry

Answer 1

Having your main logic board replaced wouldn't erase music from your hard drive, if it was actually stored on the drive. Your iTunes music resides in your user home folder in a folder called Music.
When you do get a logic board replaced, however, it is a good idea to have the computer first de-authorized from iTunes since you are only permitted to associate your iTunes Store account DRM purchases (movies, tv shows, and older digital-rights-managed music) with up to five computers. See Deauthorize your computer using iTunes.
When a new logic board is installed, you'll need to reauthorize the Mac again. It's not the end of the world, however, if this step wasn't initially taken. See Authorize your computer using iTunes.
...As for not seeing your music when you launch iTunes—try point iTunes to the correct location of your iTunes folder. To do this, quit iTunes. Press the option key and click the iTunes icon in the dock. It will then ask you to navigate to the location of your iTunes music (again usually located in the Music folder in your home folder).