no battery power in a78 corona wagon

[NeptunE3]

i got this car pretty much for free, its running and driving, 5 speed rwd, 20r motor, it looks just like a celica gt under the hood, i was running it one day and i started to drive it when suddenly no power, it just shut off, the radio shows no power and nothing works: the lights gauge wont even budge the starter, i put the battery from my escort in it so i know its not the battery...please help me