I just bought a 94 Z28. It had been sitting for about 4 years. The person I bought it from lost the keys. I got new keys for it, and when I turn the key on all of the gauges power up and everything else works. But when i try to crank the car the alarm goes off. Maybe I have the wrong code for the key? I'm not sure, any info is greatly welcomed.

 

I'm pretty sure the alarm is aftermarket, although you can check the resistor chips in the keys with an ohmmeter and compare them.

 

Try unlocking the doors with the key from the outside before you try to start it. That manually disables most alarm systems.