Diagnosis
A totally dead display with the fridge still cooling points directly to a power issue for the control board. It's not getting the 120V it needs, likely due to a blown thermal fuse on the board or a bad door switch.
How to Fix It
First, try the simplest fix. Unplug the fridge for 5 full minutes, then plug it back in. This is a hard reset for the control board. If the display lights up, you're good. If it's still dead, you'll need to check the thermal fuse on the main control board. The board is usually behind the kickplate at the bottom front of the fridge. Unplug the fridge, remove the plate, and you'll see the board. The thermal fuse is a small, white rectangular part soldered to the board. Use a multimeter to test it for continuity – if it's open (no continuity), it's blown. This requires soldering in a new fuse or replacing the entire board.
If That Didn't Work
If the fuse is good, the problem could be the display board itself (the part with the buttons) or a wiring harness between the two boards, but that's less likely.
Heads Up
Working on circuit boards requires care. Disconnect all power before you touch anything. If you're not comfortable with a multimeter or soldering, this is a good point to call a pro. A replacement control board isn't cheap, so you want to be sure before ordering.