If that's a pretty loud single clunk each time you turn the ignition switch to "crank", that's caused by a break in the high-current circuit. Usually that's worn solenoid contacts but it can also be caused by a bad battery cable. The place to start is by measuring the voltage right at the starter while the problem is occurring and a helper is turning the ignition switch. Measure right on the large stud on the starter, not the terminal on the end of the cable. If it's hard to reach, connect the voltmeter lead with a small jumper wire so you don't have to hold onto it. You can also do this by connecting the ground clip of a test light to that terminal, then poking the probe under the negative battery cable. That will give you something to watch from inside the car and you won't need a helper.
You should see 12 volts there all the time. If it goes to 0 volts and doesn't crank, check that cable and the connections on both ends. If it doesn't crank but the voltage stays there, try to measure on the braided strap coming out of the solenoid and going to the starter motor. You should see reduced battery voltage there during cranking. If you see 0 volts, the contacts are worn in the solenoid.
Wednesday, November 14th, 2012 AT 3:33 AM