Sign in window does not appear in Mac App Store.
I have been trying to work this out for a week or so. I already tried verifying and repairing disk permissions, as well as deleting the com.apple.appstore.plist file. Whenever I click the sign-in button (featured page or purchases page) nothing happens. I don't have FruitMenu or APE installed. There doesn't seem to be any help on Apple Support other than this: Mac App Store: Sign in sheet does not appear, or does not accept typed text. I have also tried downloading an app that I had previously purchased, to see if the log-in would come up, and nothing. Please Help!
MacBook Pro (15-inch, Mid 2012), OS X Mountain Lion