For diagnosing a starter that does not turn over, first ascertain that the shift lever is in neutral or park (on automatic transaxles), or the clutch pedal is depressed (on manual transaxles). Check if the battery has been charged and all cables and terminals, both at the battery and solenoid for the starter, are clean and firmly in contact. You can diagnose a problem with your battery by observing headlights; they should dim after few seconds if there is need to recharge or replace it. If ignition switch operates while lights remain bright or it dims, then current goes to the starter motor meaning that the issue lies in it. If starter motor turns slowly despite presence of good battery this implies fault in either resistance on circuit or faulty starter motor itself. Disconnect engine/transmission ground strap along with battery leads and starter/solenoid wiring for possible circuit problems. Clean them up, re-connect them back then check full battery voltage at positive lead connection of solenoid using test light/voltmeter to ensure sound grounding; apply petroleum jelly at its terminal ends so as to prevent corrosion. When starting motor spins but fails to crank engine, it means that its clutch is slipping thereby requiring replacement. In case solenoid clicks but starting motor doesn't run: double-check batteries, main contacts for solenoids used or else start gear (or look out for seizure of an engine). It could be a burnt fusible link, bad cell in a battery, defective solenoid or any other thing which makes plunger of solenoid inaudible during actuation of switch. By attaching jumper between positive (+) side of car's power source and wire terminal on ignition switch feeding into solenoid from here mentioned above you will be able to test one of these parts known as solenoid; when however armature starts moving due to supply flow from here you will feel something kicking underneath those foot pedals provided there is nothing wrong with neutral start switch or wiring inside. If starting motor still fails to operate, take the starter/solenoid unit out for further check-up and repair. Make sure that connections are tight and battery is charged properly on slow cranking starter motors. Partial engine seizure or incorrect oil viscosity may cause a slow crank. To do this, warm the engine up to normal operating temperature, disconnect the coil wire and attach a voltmeter across positive and negative posts of battery. Start it up then watch closely as voltage reading keeps on balancing subsequent in thirty seconds which should not be exceeded by started engine motor run time. A reading of 9 volts or more at cranking speed is normal. Less than 9 volts suggests potential issues with the solenoid contacts, starter motor, discharged battery or poor connections.