HELP! my 94 Z28 will not start. when I turn the key and the security light comes on. I have tried 3 different keys and nothing works.

 

Either the chip in ALL the keys are bad or there is something wrong at the column. If you want to be done with the problem for good and don't mind doing away with the security of the key chip you could do the following.

Measure the resistance of the chip in the key that normally works in car. Now buy a resistor with that value at Radio Shack. At the base of the steering colum there is a yellow 2 pin connector. Pull it apart and put the resistor in the end that does not go to the steering wheel. Wrap it with tape and you're done.