Diagnosis
This is a classic blown main fuse or a failed control board. The hum is the transformer but the low-voltage power supply to the electronics is dead.
How to Fix It
Unplug the microwave. Remove the outer case. Locate the main fuse on the control board or near the power entry. It's a glass 15A 250V fuse. Test it for continuity with a multimeter. If the fuse is blown, replace it with an identical fuse. Reassemble and test.
If That Didn't Work
If the new fuse blows immediately or the display is still dead, the control board is faulty. It needs to be replaced as a unit. Part number is often W104 or similar on the board itself.
Heads Up
Do not jumper the fuse. A blown fuse is a symptom. If the magnetron or high-voltage circuit is shorted, a new fuse will just blow again. High-voltage capacitors inside hold a lethal charge even when unplugged.