2000 trooper wont start!!! pulled it in the driveway shut it off then wen't to leave and wouldn't start. i changed the starter relay and still nothing. makes a clicking noise and that is it. is there a security code making it not start?

I had the same problem and found that when I took the battery terminals off and cleaned them the starter worked perfectly. Beware that you have the radio code as you will need it if the battery is disconnected.

Sounds like the starter solenoid is working, but the starter motor isn't. If you have a voltmeter or test light, measure for light/12 volts at the motor terminal while someone tries the key. If the solenoid is what is 'clicking', but nothing at the motor terminal, change the solenoid. If you get light/12 volts, then the motor itself is in trouble.