I've got a 1996 Buick Regal that starts everytime you turn the key, but shuts off 3-5 seconds later

We got a new key for it and a new ignition coil for it in case the connections were bad too but the problem still continues. The security light stays on and the check engine light is on. I know if the computer isn't seeing the engine running, it won't run the fuel pump, but how do I check the Cam and Crank position sensors so I'm not just throwing parts at it. Also could it still be a security issue? And how do I check that?