Yeah, this one's common. The motor is getting power but can't start, usually due to voltage or internal friction.
First, unplug any extension cord you're using. Plug the unit directly into a 120V outlet. Voltage loss from a long or thin extension cord will cause a buzz with no start. Verify that only the pressure washer is running on this circuit.
If it's plugged in directly and still buzzes, there might be residual friction if it hasn't been used in a while. Disconnect the water supply, then turn the power ON for just 2 to 3 seconds. Turn it off, wait, and repeat a couple times. This can free up the components.
If that doesn't work after a few tries, the unit might have a tripped internal breaker or other fault. Let it cool completely and try again. If it still fails, you'll need to call customer service.