WINDOW:

      - navigator, histogram ...
      - history, actions ...

      - layers, channel ...

If Photoshop starts acting weird, the first thing to do is delete Photoshop's Preferences file and restart Photoshop. This will build a factory-fresh set of Preferences that will usually cure the problem.

Now, Photoshop can make this "trashing-the-Prefs" routine even easier. Just hold the Shift-Alt-Control keys when you first launch Photoshop, a dialog box allowing you to delete the Photoshop settings file. Click OK, and Photoshop will then build a new, factory-fresh set of Prefs for you.