Did you try moving the monitor to the other video port? It sounds like you had it running dual monitors at one time and you removed the display listed as "display 1" without setting the desktop back to a single monitor first.
You could also hook the other monitor back up so it is a dual display, then go into the desktop setting and switch it back to a single display, then remove the second display.
No I never configured it to run 2 monitors. I blame that on the cat. When I booted up the task bar wouldn't show but all the desktop icons were there. In order to get the task bar to show I push a button on the side of the monitor. Then the task bar would show and all the icons would disappear. I couldn't do anything in this mode. Finally I rebooted. Right click. Hit screen resolution and chose use 1 desktop.
You got a cat at home that can configure multi monitors on a computer?! Wow!
Well, try rebooting the computer, then before the "Starting windows" appears, press "F8" repeatedly until a menu appears. If it prompts you to select an operating system, press F8 one more time, that should bring up another menu. Use arrow keys to select "Enable low-resolution mode" and press enter. It should boot.
Note that everything should be very big on your screen now, but you should be able to reset the settings that way