Diagnosis
PF stands for Power Failure. The microwave's clock board lost power briefly, and it's stuck in a reset state, usually from a brownout or a tripped circuit.
How to Fix It
You need to perform a full power reset. 1) Unplug the microwave from the wall outlet. 2) Wait a full 60 seconds. 3) Plug it firmly back in. 4) Immediately press the 'Clock' or 'Kitchen Timer' button to set the time of day. Once the clock is set, the PF message should clear and normal functions will return.
If That Didn't Work
If the PF message comes back immediately or the unit is completely dead, check your kitchen's 20-amp circuit breaker. It's possible the breaker tripped or is faulty. Reset it firmly to the OFF position, then back ON. Also, ensure nothing else is overloading that same circuit.
Heads Up
If PF becomes a frequent problem, it's often a sign of unstable voltage in your home (like from a sump pump or AC unit kicking on) or a failing control board. Using a dedicated outlet for the microwave is ideal.