Alienware x51 Black screen with cursor while installing Windows 10 – Windows 10 Forums
If you have an Alienware X51 and want windows 10, this is for YOU!
Essentially; post install of Windows 10, the Screen is going to be on the ON-BOARD video; not your good video card, so you need to hook up an HDMI cable to the HDMI port on the back of your unit and proceed from there, then DISABLE that video card in Windows once you are done.