1988 Supra electrical prolblems

A few weeks ago i bought a 88 supra. it needed some work but not much, but all of the sudden it wont crank...and my relays (i think) are all fine. when you turn the key to the "ON" position, everything works. and so does my radio. but when you turn the key to start the car, it doesn't do anything. but the only that is wrong is that the clock dims when the key is turned to the start position....someone please help me ASAP!!