Many forget to install Dell's QUICKSET software and then have this and other issues.
Then you have driver problems. Since it's a Dell you head to dell.com, input the machine's service tag and there are the drivers. I know many forget that it is that easy.
I have a Dell laptop, and a Dell 1701 Monitor. I have the monitor plugged into the CRT/LCD port on the laptop while at home. For a while, I could get them both to display by hitting the FN & CRT/LCD keys. I could not toggle these keys to get only one or the other or both to display (as you can normally do with n LCD projector). Now I cannot get the desktop monitor to display anything. I may have turned on the monitor extension function to work, when trying to troubleshoot this problem, but now I cannot turn that function off, even though that's not the function I want.
Also of note: when I check Computer Management I find that I have 2 entries under display adapters - both say "Intel 82852/82855 GM/GME Graphics Controller" - both are enabled. I don't think I shold have 2 controllers in a laptop.
Also I have duplicate Monitors: I have 3 identical entries for Plug and Play MOnitor (the laptop display), and 2 entried for my attached DEll 1701FP (analog). the External Display