1. What happens when you attempt to boot into "Safe Mode"?
2. Do you think you setup a dual-monitor display system? Was this done thru display properties where you have two little monitor windows and you selected the external as the "primary"?
3. Does your current screen have a "task bar" at the bottom? If so, what happens if you move to the task bar, right click, select Toolbars, and click on "Desktop". If this works and adds a desktop toolbar where you can access it, you should be able to work your way to display properties and correct.
4. Does the ALT-Tab key combination display your open programs on your current window and allow you to cycle through them with each repetion of ALT-Tab?
5. When you boot the laptop do you see a logo or Power On Self Test (POST) diagnostic messages on your current screen? If not, are you able to reboot and enter CMOS setup on your current screen? If so, there may be a BIOS setting to select your POST display. What are the options and what does it currently say?
6. In the land of the blind, the one-eyed man is king... Or not...