How much RAM and spare hard-disk capacity do you have?

Try resetting the Preferences back to the factory defaults to see if that sorts the issue out (if it doesn't, uninstall Photoshop and reinstall it again). 

You reset the Preferences under the General Tab in Photoshop Settings, then Close and reopen the application.

If you can’t reset the Preferences because you can't launch Photoshop, you can do it manually:
Launch Photoshop and quickly hold down the following keys: 

Windows: Shift+Ctrl+Alt 
Mac OS: Shift+Control+Option+Command 

When prompted to delete the Preferences, click Yes 
(If you don't see the question repeat the exercise.)