Security light on

I am not sure if my battery went dead or what happened, but I put a charger on and made sure it has a full charge. The problem being the only thing that worked when I found it this way was the security light was on. Charged completely, the security light remained on and the rest of the truck remains dead. Can only unlock with the key, no lights, no anything and after trying to start it the security light went out, but everything remains dead. Do not have any idea what to do now.