Welcome to JUST ANSWER small engines, let me try to help you !! When did mower last start? You say you checked the battery. Have you checked the battery cables on both ends, especially the negative cable at the frame connection. The starter solenoid is part of the starter, have you checked to see if you are getting power to the switch side of the starter when the key is turned to start? You can check with test light or voltmeter. The 325 also has a neutral switch on the transmission, maybe loose connection there?