When something goes wrong and Photoshop isn’t working the way you expect, there’s a panic button. Before you reinstall Photoshop as a drastic last resort, you can try resetting the preferences file. Often, there’s a bad preference that has clogged the system. (Occasionally, you turned on a “feature” by mistake.) Resetting the “prefs,” as we call it, will fix the majority of technical issues you might have with Photoshop. Important note: Make sure you back up all your custom presets, shapes, patterns, and such before you do this.
You can find the preferences file in Window/System
/Application Support—just kidding, this wouldn’t be a tips column if I didn’t have an easier way, would it? First, quit Photoshop. Then, hold down Shift-Command-Option (PC: Shift-Ctrl-Alt) and click the Photoshop icon; you know, the one you use to start Photoshop. Photoshop will now ask, “Delete the Adobe Photoshop Settings File?” Choose Yes. Photoshop will now start up and, hopefully, behave itself this time.