If power button turns white, that means the PC successfully completed the POST (power on self test). Can you test this monitor on a different PC or a different monitor on this PC? Do you have an add-in video card (either NVidia or AMD) or only use onboard ("integrated") Intel HD Graphics? If you have an add-in video card, are you sure the monitor is connected to the card, not to either the onboard HDMI or DIsplayPort ports? If you have only one monitor, it has to be connected to the add-in video card. The onboard HDMI and DisplayPort ports don't work unless at least one monitor is connected to the add-in video card. The onboard video ports are in the area marked 1. The add-in video card is marked 2: [IMAGE]
My computer will not boot to windows when starting up. The computer will turn on, but nothing will appear on the screen. I do not see the Dell logo and it does not boot to Windows. I have to do several hard resets before it will boot successfully. Once working, it will work fine if I restart the machine, but will encounter the same problem if the computer is idle overnight.  I have already tried turning off "Fast Startup" and  changed the CMOS battery. Stock XPS 8920 with not modifications. 
XPS 8920, BIOS update 1.0.23, black screen on startup