Gen will not crank

Make? Model? I just went through that with my Onan Marquis 5.5BGM. Do you hear anything when you push the button? Clicking? Fuel pump running? First check is battery power. Get a voltmeter and test the battery voltage at the batteries. Should be around 13VDC. If not good, try jumping them with a known good battery, or simply replace them. If battery voltage is good, then test the voltage at the generator. If not good, check all cables/fittings for good connections, tightness and lack of corrosion. Clean all connections if necessary to remove all corrosion and reconnect. If that's all good, then check the solenoid. You can test it by using a heavy cable (like jumper cables) and jumping across the main terminals. If the engine turns over, then your solenoid is bad. If it doesn't, then you may well have a bad starter motor.

Again, post the make and model and you might get more assistance.