Sometimes Photoshop may start acting up and may start to cause problems that weren't there before or Photoshop might become corrupt. One simple fix to a variety of problems is to Delete the settings file and have Photoshop create a brand new one.
To do this hold down the following keys while the program starts:
You should be prompted with a dialog box that says: "Delete the Adobe settings file?" Click ok and the program will continue to start, then upon start-up it will ask you if you wish to configure your color settings. If you don't want to do that, say yes anyway, then when the new dialog box comes up just click "OK". And Photoshop will act as if it has just been installed.
If you don't get the dialog box asking if you wish to delete the settings file, then you didn't hold down the key command early enough. Close Photoshop and try again.