Security system on my car

So I had an issue where nothing worked but my
lights and radio. I thought it was the ecm because
it suddenly dropped to 7mpg, door locks locked on
there own, and temp tack read cold the last 3 days.
While it was running. So I thought try resetting it. I
was disconnecting the positive lead when I hit it. It
wouldnt do anything. Would start the fuel pump
stayed off. Pulled the ecm out and i did a smell
test for burnt wires. Didn't smell anything. Fuses
and relays are good. Put it back together and now
it turns over again. Fuel pumps working. I guess
my question is there any anti-theft/Security thing
keeping it from firing? There's no light flashing for
that. Just says reduced engine power