Resetting your Preferences
On a Mac: Right after you double click on the icon to start the program, hold down Command, Option, Shift keys all together. If it works it will come up with a little dialog box asking if you want to delete your preferences file. Click yes. If it didn't work, you probably didn't press the keys fast enough, and PSE will just start up normally. Shut it down and try again.
On a PC: Same instructions as above, but press and hold ALT, CONTROL, and SHIFT.