I'd suggest using some jumper wires to the (unplugged) solenoid wires (which are probably Green/Red and Yellow/Red or maybe Black/Yellow) on the solenoid itself to see if it 'clicks' when applying power to them. That will tell you if the solenoid is moving inside. If it isn't, you can disassemble it and clean up the [likely corroded] shaft for the plunger so it can move again. When these sit for more than 7 or 8 years unused, the plunger shaft offten corrodes and loks itself still.