Hey man I tried to IM you back, but I lost it so I will write it here. I think Tengram is right about the switch which is what the key activates, but lets check to see if everything is wired right. I don't know why there is a ground wire on the solenoid. Your ignition switch in your column gets power from the battery cable side of the solenoid. It then sends power to the coil, the accessory fuses, the hego, the idiot lights, the eec relay, and the ignition wire on the solenoid (little wire on top). Looking at the solenoid form the drivers side of the car, on the front there should be a cable going to the starter. On the back post, there should be a yellow cable (supplies power to the ignition), the battery cable (positive), and some other wires. The ground cable should be grounded to the engine block. How it works is, when you turn the key to the on position it sends power to all that stuff I mentioned except the ignition wire. When you turn it to the start position, it sends power to the ignition wire to the solenoid. The solenoid is grounded to the fender. There is a little coil inside the solenoid that is magnetized when the power flows thru from the ignition wire. The magnet closes a switch in the solenoid between the front post and the back post and causes the starter to get power. When the key is released back to the run position the power is cut from the ignition wire and demagnetizes the switch in the solenoid. I would start by checking all the wires to make sure they are hooked up correctly and are in good shape. Then I would start checking the system to find out where it is bad. Take the ignition wire off the solenoid. Hook up the cables and see if it cranks. If not then the ignition switch is more than likely bad. If it does crank, then the solenoid is more than likely bad or something is wrong with the wiring. If it cranks you will still need to check the ignition switch because that could be causing the solenoid switch to go bad. To do this, take the cables off the rear of the solenoid (the battery cable side), take the ignition wire off the top of the solenoid, connect the battery cable to the ignition switch cable (should be yellow), hook up the battery, test the ignition wire for power with a test light. No power the switch is good. All these tests are with the key turned off. Now if by some chance you have a mini starter, let me know and I will tell you what would be different about the wiring. Good luck, and I hope this is not confusing.
http://img72.imageshack.us/my.php?image=solenoidxa0.jpg