If the starter does not rotate when the switch is operated, it should be checked that the speed selector lever is set to 'N' or 'P' if it is an automatic transmission, and that the front seat belts are connected and that clutch pedal, if any, should be pressed down. Check that the battery is well charged, as well as all cables connected to the battery and starter solenoid terminals. If the starter spins and the engine does not crank, the over running clutch in the starter may be slipping, and, in this case, the starter assembly has to be removed and dismantled. If the starter will not turn around and if a loud 'click' is heard to have come from the solenoid plunger, then most probably the problem is with the main solenoid contact or the starter. If no sound is produced in the solenoid plunger there is tendency that it has a defect or the circuit is opened. The solenoid shall be tested through joining a jumper leading between the solenoid terminal and the battery positive terminal holding the purple cable; if the starter runs successfully, then the solenoid is fine therefore the problem is probably with the switch ignition or neutral start or the wiring of the switch ignition or neutral start. If the starter will still not turn on then have the starter/solenoid assembly pulled out for examination and repair if necessary. If the starter turns the engine slowly, then the battery may be dead, or the connections loose or the engine oil could be of the wrong grade, or there could be some other problems with the engine. Warming up the engine to the normal operating temperature, switch off the engine and to eliminate the firing during cranking, remove the coil to distributor LT wire. Attach one probe of voltmeter to the starter terminal of the solenoid the other probe to a good ground point, turn on the ignition switch and take reading as soon as a steady readings are obtained without engaging the starter for more that 30 seconds. If the reading is 9 volts or more at normal cranking speed, the battery is in good condition/ if the above reading is 9 volts or more, but cranking speed is slow, it is the starter. If its having a below 9 volts reading and if cranking speed is bad then there is chance of solenoid contacts to get replaced.