thorpedo91

I want to start with a little back round to give an accurate description of my problem.
I recently rebuilt my engine and transmission. I reattached all my lights, and electrical systems, everything working fine( except for one broken headlight bulb and taillight bulb). I have took it on a very short ( about 100 yards) trip to the gas station a couple weeks ago, the first time actually driving it. Everything was working great.
Today, I drove it to the same gas station, and back. parked it for a couple of hours, and replaced the taillight bulb. Started it right up, drove about a mile round trip around town just to make sure it sounded fine and was working great. Parked it back at home, turned it off, and got all the stuff i needed to load into the car. Started it back up, no problem, about 10 minutes from when i turned it off. drove a mile down the road and parked it for 5 minutes. when i come out to start it up, it won't start.
I put the key in and turn it to on position, and it the dash lights up, interior lights come on, and if the doors is open, the buzzer goes off telling me my key is in the ignition. The second I try to crank it everything shuts down. If i leave it off for a random amount of time( it varied from 10 seconds to 10 minutes) I can put the key in, and have dash, interior lights working as well as buzzer.
From this point, if i do any of the three following things, everything turns off. If i tap the brakes, turn on the headlights, or try to crank the engine. I have no idea whats wrong. please help

70 cutlass s

Check your ground. Start first at the battery first clean the post and make sure the end is tight. Then other end of the cable make sure its tight. Make sure its making good contact. Might have to take it loose clean some paint off bolt the cable back up. Check the cable make sure the cable is not bare any where. Also check your body ground at the firewall make sure its not broke and bolted to the block.