Diagnosis
It's almost always a power supply issue, not the unit itself. The cord or plug is faulty, the outlet is dead, or the unit's internal fuse has blown from a power surge.
How to Fix It
Work from the wall inward. 1) Test the outlet with a lamp or phone charger to confirm it's live. 2) Check the AC's power cord thoroughly for any cuts, kinks, or damage, especially near the plug and where it enters the unit. 3) Ensure the plug is fully seated in the unit's socket—it can look connected but not be. 4) Try a different, known-good outlet on a different circuit.
If That Didn't Work
There's a small thermal fuse inside, often on the control board, that can blow. Accessing and testing this requires taking off the cabinet and using a multimeter. If you're not comfortable with that, it's time for a service call.
Heads Up
These units draw a lot of power. Always plug them directly into a wall outlet, not a power strip or extension cord, unless it's a heavy-duty, short cord rated for 15 amps. A weak cord can overheat and cause this.