2002 Toyota Camry totally dead car

I stopped at a store on the way home, and while my son went in for a couple of minites I listened to the radio with the engine off. When he came out, I tried to start the car but it didn't make a sound. In fact absolutely no electrical anything worked. I called a tow truck and he tried to jump start it but the car stayed dead. I had the battery tested and replaced it. I installed it and the only thing that worked momentarily was the door ajar indicator on the dash display. After a few seconds of display it went off too. I disconnected the battery so as not to have it drain, and now I'm thinking. Could it be the computer? I really can't afford to replace it now. Can you assist me? Thank-you, Chris