RESETTING PHOTOSHOP'S PREFERENCES
Here's a quick way to reset your preferences in Photoshop: Press-and-hold Command-Option-Shift (PC: Ctrl-Alt-Shift) while you start Photoshop. As you start the program you will get a pop-up dialog asking you if you would like to delete the settings file. Deleting the file will create a new set of preferences from scratch.
Great quick tip on resetting preferences.