Start Photoshop and immediately hold down Ctrl+Alt+Shift If you do it in time and Photoshop will ask if you want to delete you preferences reply yes. Photoshop will then delete them and generate a new set of preferences with Adobe default setting. When Photoshop starts to act strangely it often because a preference file has become corrupt. It such a common problem Adoebe added the shortcut key combo to help you to reset your preferences.
When I get Photoshop working like I like I back up my Preferences and when Photoshop acts strangle I exit Photoshop and replace my preferences files with my bacup copy.