1994 Hyundai Scoupe

hi what is wrong with my car? last night when i was driving it the radio just turned off, then when waiting at the light my car lights and dashboard clock began to dim and turn off and then when i pulled over and turned off my car it wouldnt start up again, but then after waiting for a while i could turn the radio on but when i turned my lights at the same time on they worked but the radio shuts off once something else is being used like windows or when i press the brake. but the car still wont turn on. i have people saying its a bad battery, some saying it's electrical.... can you help me?