If the battery is in good condition and fully charged, Be sure the battery wires are clean and tight. Check the ground wire going to the engine, from the battery by the starter to be sure it is clean and tight too. If it still doesn't turn over follow the Red+ wire to the sealed electrical box and open it. Use a 14 guage jumper wire, jump across the starter solenoid. If the starter does rotate over the solenoid is bad. If the starter doesn't turn over the starter might be bad.
Karl