97 cadillac deville starting disabled car will not restart.

This is the part that you will need to take care of that anti theft issue.. Do It Yourself GM Security bypass

put key in drivers door that will disable it

lock and unlock drivers side door with the key will disable the alarm system

If it is anything like the expedition I own there is a chip in the key that needs to match the ignition for the vehicle to start.

you either have a bad key...did you try more than one key?
Two other things can be wrong..
1) the igintion cylnder (where ya put the key in) has samll wires that sense the pellet in the keys for your car, and often they break, and the cylnder has to be replaced.
2) the passkey module has gone bad.
Either of these problems can be fixed by any compatent mechanic that has cadillac experience.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

have you tried to get your key looked at??
maybe the resistor on it is no good anymore,
or maybe the wires for this system are damaged,
they are two skinny white wires inside an orange sleeve
(that's how it is on my 97 deville)
check under the dash.

Replace ing. lock cylinder and key.

I had the same problem. trying to save money i took it to several auto places who thought they could fix it..... after a lot of money and my 800.00 after market alarm was taken off i had it took to the dealer . They fix it in two hours they put in new switch and key haven't had any problems sence.

Try cleaning the key "chip" resistor and if this doesn't work try the other key.

the wire that goes to the ignition to the anti theft device is probably broken if you call a good locksmith they can go in through the steering column and fix it same thing happened to my 95 eldorado apparently cadillac designed the anti theft system to coincide with the ignition and is connected to the ignition with two wires that turn as the key is turned the wires twist and eventually they wear out