First make sure the starter mounting bolts are tight. Then make sure the battery is fully charged and in good condition. Have it tested, if necessary. Full voltage should reach the solenoid; otherwise there's a problem in the circuit. Also, a faulty solenoid could be the problem. You can check for power at the solenoid once the ignition key is released when starting the engine. Be very careful with moving components when doing this. And make sure the car will not move. Test for power at the solenoid cables. If there's power with the ignition key released (at "run" or when off) then check the ignition switch (possibly a short). If there's no power, then the problem is with the solenoid. Hope this helps.