Car will not start. No electrial power

I have a 1989 Supra turbo that has lost all electric power. The battery is fully charged yet there is no eletric power being distributed to the car. Everthing except the front headlights is dead. You turn the ignition and nothing happens. It is as if there were no battery in the car. I did check some of the fuses and circuit breakers and found nothing blown. The fact that nothing works leads me to believe there may be one primary distribution point for power where the problem lies. Can anyone help with this or give me some idea where to start trouble shoooting? One last thing that might help. Yesterday the battery was weak and my son tried to jump start it. He could not get it started and I am somewhat suspicious that he may have connected the positive terminal to the negative terminal when he was trying to jump start the car. He swears he did not but it's a possibility. If this were the case can anyone tell me what may have been damaged? THANKS

hey hows it going im not sure but i had the same problem where my battery was hooked up wrong but my car has power i just blew a few fuses and now my car doesnt get fuel.my guess is check the fuseible links.and check that the battery is on correct if you didnt do so already when that happen to me just my lights turned on but didnt crank also check you relays in the engine compartment you have main relays in there as well good luck hope i was some help.