Had the same issue on my Whoa Nellie. Just have to carefully remove apron and push in the mini display cable connector. They tend to jiggle loose from that display.

However have them study the manual. I accidentally plugged the cable flipped in the wrong direction. Entire machine popped and went completely black. I skipped a few breaths thinking I blew up the machine, but after I unplugged the mini display, the machine booted up again. So, make sure the connection is in the right orientation.

Cheers