Need to uncheck "extend desktop" in monitor properties

Running home xp on Dell 8250 no problems for several months until today. I attached an external hard drive to usb port, computer stopped responding, I restarted and now have got an extended desktop which I don't want. Went to desktop properties/settings and the "extend the desktop" is checked and grayed out. I tried changing to the secondary monitor to try to uncheck it but wasn't able to. I am in the process of scanning and printing out several wedding photos and need the stationery screen. Any help is appreciated.

 

check your bios settings for your video card they may have changed

 

Thanks so much for your replies. After worrying about working on my photos after my post, I decided to just try restarting the computer. Sure enough everything went back to normal. Many times restarting takes care of some problems. I will keep in mind your suggestions if the problem comes up again. Thanks again.