(Liaison for Desktops, Alienware, Monitors)Would you like to be a Dell Community Rockstar?
Had a very similar problem.
Two weeks trying to get resolution through traditional Dell Support.
Finally they suggested "we may need to do a system restore - which will return your computer to the way it was the day you took it out of the box."
aka: You are going to have to wipe it clean, and reinstall everything - programs, data, and setting.
That became a great incentive to look alternatives.
Try this process... (Pieced together from other posts)... It worked for me
Go to control panel - power options.
Change plan options.
Change "Turn off display" to: Never
Shut down system.
Power off BOTH displays during shutdown process.
Wait at least a minute or two...In this order:Power on both monitors.
Power on system.
If second monitor doesn't appear (which is likely)
Right click on desktop
Select Display Settings
Click on "Monitor 2"
Click Extend the desktop...
If the monitor doesn't appear - repeat the power-off/restart routine.
You may also need to make a chance on your video card control panel.