NO START, CHECK ENGINE LIGHT ON AND OFF, THEFT WARNING LIGHT ON

The theft warning light is the big clue. Most late 90's GM vehicles are equipped with VATS (Vehicle Anti-Theft System) If your key has a chip on it (assuming you are using the correct key) then a really common failure are for the two 24ga wires that attach to the ignition lock cylinder to fail. They twist with each key revolution and easily break. Unfortunately they are inside the column so the column will have come apart to repair it. There are other anti-theft systems (no chip in this case) and there are other possible causes, the best answer it have it towed to a shop for diagnosis.

you can try a relearn process first... turn key to "on", leave for 30 min. exactly turn key to off for 10 min exactly. repeat 2 more times. then remove key from ignition. let sit about 30 sec to a min. then try to start. if that doesn't work try to clean the metal ends, both sides, visable on key with a small nail file, using the not so rough side. lightly run across metal portion about 3 times. this cleans the contacts allowing the elec signal to be sent fully to start car. it worked for me, tried on first set of keys, worked. tried spare key w/o doing the filing and it didn't work. filed and it started. been working everyday, all day for last 3 months. hope it works for you, will keep about $150-$200 in your pocket.