Verify the power switch is in the "I" ("on") position. Although apparently simple, forgetting to switch on the pressure washer is surprisingly common.
Confirm the pressure washer is plugged into a working electrical outlet. Check the outlet is switched on if your household outlets are fitted with on/off switches.
Replace the extension cord with either a 25-foot 12/3-gauge cord or a 50-foot 10/3-gauge cord. Other types of extension cords may not work with your Karcher washer.
Check your fuses or circuit breakers. Some of your electrical circuits may not be functioning due to a blown fuse or tripped breaker. Verify that all fuses or breakers are active.