Won't start

I don't have the answer, that's why I'm asking you.

?????

Have you cleaned and tightened the battery terminal connections? Do the lights come on or is everything normal except no cranking over?

Going by the age of the vehicle, and the symptoms, you may have a failed security system. The security system is notoriously known to fail. Basically when you insert your key, the system checks for a certain signal. If the system cannot get the correct signal from the key, it assumes the key is incorrect or you are attempting to hotwire it. The system then goes into SECURITY lockout mode. (prevents vehicle theft) This will either turn off the starter, or the fuel injectors. This has been happening with GM's for a very long time. There are ways to bypass this now. Read through this page for info, solutions as well. http://www.diy-gm-security.com/