To find the starter solenoid, follow the wire from the starter up. This will lead to the starter solenoid. Traditionally there are two big wires bolted to the soleniod and a third relay wire (controlled by the ignition switch) going into the solenoid that activates the soleniod and makes the connection between the two big wires. One of the big wires going to the solenoid should have about a 12-14 volt constant charge even when the car is off. This wire goes directly to the battery.
So what you can do is take a big screw driver and or heavy guage wire and make a connection (jump) between the two big wires going to the solenoid, this will supply a direct voltage to the starter. The starter should crank over like normal with a 12 volt charge directly to it, bypassing the solenoid. If that works, then the solenoid isn't working properly.
If nothing happens try using a jumper cable connected from the positive lead on the battery and apply the other end to the power lead on the starter this should turn the starter over.
You can try these options with the ignition off and the car won't start up, just turn over. Or, with the ignition on and the car will start and run but the starter will not turn off until you remove the 12 volt power source.
Just be carefull not to be in the way of any moving parts!!!! | 
