I have an MTD Yard MAchine. It will not crank. I get nothing when I turn the key. Battery is good. I'm thinking it is the solenoid valve. Does anyone know how to check the solenoid valve.

Cross the two main posts with a screw driver(it will spark so don't be surprised)if the engine turns over when you do that it your solenoid (could be your key switch and wiring too ,not sending the message to the solenoid to connect the power)

Are you referring to the anti fire solenoid, or commonly known as the fuel solenoid? If so, remove the wire(s), remove the solenoid from the fuel bowl, hold the solenoid against the body of the engine to ground it, hook up the wire(s) and turn the key. If it moves up and down in response to the key being turned on and off, it is working. Sometimes, the solenoid will benefit from being cleaned on the piston rod, and lube.