Caddy won't start

In out auto class today, we replaced the computer on a 2000 Caddilac Deville. It wouldn't start before and it still won't start now. The security light comes on and when you try and start it, the lights in dash go out. The battery is good. Anyone have any ideas?

i think once you change your computers you need to clear the security codes again i do believe.

The keys will need to be reprogrammed to the new computer. And did you also reprogram the computer after you put it in? Alot of PCM/ECM's have to be flashed with a Tech 2 before they are operational.

The computer was suspose to be reprogramed by the place we got it from. I glanced over alldatapro to see if I could find anything and it did mention something about the keys. how do you reprogram the key?