I have a Mac Pro 1,1 running OS El Capitan 11.2 and iTunes 12.4. I tried to do the most recent update to 11.5 which failed. I used the Disk recovery to reinstall 11.2. Since then, none of the 4 accounts on my computer can sign into iTunes. There are multiple places in iTunes that one can click on that require you sign into your account. When I click any of those, simply nothing happens. No error messages, simply nothing. I tried to go back to a previous version of iTunes, but my library has been updated and it won't let me. Any suggestions?