Diagnosis
The control board is locked up. This is a reset state, often triggered by a brief power interruption or a voltage spike.
How to Fix It
Perform a full power reset. Unplug the microwave from the wall outlet. Wait for a full five minutes. This discharges all internal capacitors. Plug the unit back in. The display should clear and return to standby.
If That Didn't Work
The main control board may have a persistent fault. With the unit unplugged, check the kitchen circuit breaker for the outlet. Reset it if tripped. Plug a different appliance into the outlet to confirm power.
Heads Up
If '88:88' recurs frequently, the outlet or home wiring may have unstable voltage. Consider a dedicated outlet or surge protector.