If the starter is engaging this means everything is working like it should and possible problems could be a loose connection going from the starter to battery positive or possibly your engine is seized up not allowing the starter to turn. You can use a voltmeter to verify the small terminal on the starter gets voltage when key is in crank position and also make sure the large terminal has voltage at all times. Then you can do a voltage drop test which tells the difference in voltage at two points to let you know if the problem is a loose connection. To do a voltage drop test you put on lead of the voltmeter on battery positive and the other lead on the large terminal at the starter and try to start it. The reading you see on the voltmeter will show the difference in voltages it should be low, if its large then clean or replace the large wire if its low then this means the engine may have seized and you will want to try and turn the engine over by the crank to see if you can you could also try to remove the spark plugs to relieve compression. Let me know if you have questions, thanks.