Someone who has Nik plugins installed will need to address the original issue.
"The Home icon is also greyed out, and the help menu is not responding" -- Ps or Nik app?
Are you logged into Creative Cloud?And with the same e-mail account?
Many versions ago, I had a problem with Ps because I had ignorantly used different e-mail accounts to log into Ps and CC.
I'm Grasping at straws again.
P.S. when Nik was uninstalled (if it was Ps that Home and Help was grayed out), were h&H grayed out?
Solved. I did a reformat of my hd and reinstalled osx. Photoshop works without problems. I had set up my new machine by migrating from an older machine. I guess that was the problem.