DIAGNOSIS The inverter board isn't sensing the engine RPM to enable AC output. Usually a failed RPM sensor or its connection.
FIX Check the RPM sensor and its wiring.
1. Let the engine cool. Locate the RPM sensor on the flywheel shroud.
2. Trace its thin two-wire connector back to the inverter board.
3. Ensure both connections are tight and the wires aren't pinched or frayed.
4. If connections are good, the sensor itself may need replacement.
IF THAT DIDN'T WORK A less common cause is a tripped GFCI. Press the "Test" and then "Reset" buttons on the 120V 20A duplex outlet.
HEADS UP Never run the generator with a load connected while troubleshooting no power. Start and stabilize with nothing plugged in.