no crank, no power, key locks, shifter locks

My girlfriend has a 97 grand prix se. 3.8. The car will not start, turn over, key locks in the ignition, shifter locks, and no power to anything. No fuel pump nothing. All I get is power to the radio, dome light and ding ding from door open. I have been tryin to figure this out for 2 weeks on my spare time. Im stumped. I can leave the negitive cable off the battery for 8 plus hours and reconnect and it will start as if nothing ever happened. I replaced the battery and check numerous wires. Im not going to lie, this cars prior owner treated it like crap. There is some shaddy stuff iv seen on it. I can only figure the PCM is going out or some theft deterrent system is doing this but no theft light is shown. If anyone has ran into this problem, or knows what I might need to do, I would greatly appreciate it. Thanks, and more info can be provided if need be.

Check your grounds maybe?

I have checked grounds and besides that wouldn't explain why I can start it after the battery has to be disconnected for 8+ hrs with no problems... other than the fact it dies on the road or won't restart after 5 mins of driving.

Have you pulled the battery cables off, removed the bolts from teh rubber boots, removed the boots and looked at the cables?

I'm thinking either that or an ignition switch.

Yes I have cleaned the cables, I have checked the ignition switch. It checks out fine after I have left the batt cables off for 12hrs. But as soon as it does this crazy thing it dosnt have power, but thats to be expected because almost everything else dosnt either. I still think it is a theft deterrent thing (although there isnt a security light flashing) or perhaps its a capacitor in the ECM going bad and so when the power is removed it drains the capacitor and erases the memory of the ECM. No one has ever had this happen before? I asked an AMT mechanic trained in pontiac and he dosnt have any good answers either. All the symptoms go back to the fact that everything is fine after the batter is disconnected for 8+ hrs. but once driving or parked the car engine will either die or if trying to start, it wont have power to anything for no reason at all. If anyone knows anyone who is a mad scientist at the electrical department of these cars please ask them for me or have them post a reply on here. Thanks again for the ideas and sugestions.

Ya know.if you look at the schematic....all power is routed through the known to be flakey as hell ignition switch. The BCM can't control all the stuff you mention either. The pcm doesn't control power to most fo the stuff you mention. So I'd rule those two out by basic default that they dont' control that stuff

i have seen on my car where the Positive battery cable can rub against the AC lines and short out. it could be something that when there is current for a while it will heat up and then short. but when powered down for the 8+ hrs it drops the connection and needs to heat up again to short.

try this... get it running and when it dies use a volt meter to test if the positive cable shorts to ground. test the ignition switch. test it all. and compare it to how it is after sitting for the 8+ hrs obviously when you find the diff you found the cause.

is there an ignition/ starter relay that could be bad?

On a 97 Prix, sure. The pnp switch on top of the trans under the selector lever is a starter relay. It keep the car from being started in anything but P or N. But..that won't kill power to all the things being disrupted in the post.

thanks guys, I will check your ideas and let you know.

Just an update. Car still wont start or crank and no power after replacing the ignition switch. I replaced the ECM after next and it worked. Started and stopped 3 times. Locked the car and went inside. Next day came out and its back to its old problems. I have pulled the lock key cylinder out and cleaned it, no help. I looked up and found that there is a way to change the modes of the Theft Deterent system. ((It says to remove the MALL PGM fuse, Turn key to ACC, and the seat belt light will flash and you will hear 1 to 4 "bong" chime telling you the mode the theft deterent is in. Then it says to turn on and off the "parking light switch" to cycle through the 4 modes. Once the mode of choise is picked, turn off key and reinstall the MALL PGM fuse.)) Now I was not able to get it to do any of this the way it they said. I removed the MALL PGM fuse, turned the key to the "RUN" position, and was able to get the chime. I had to use the dome light switch to cycle through the modes. I picked mode 3, which is all disabled. Turned off the key and reinstalled the MALL PGM fuse. "Nothing" I went back to through the cycle I had done and found out it never saved on mode 3. I am stumped and time is starting to become an issue. Please, someone help. All the symtoms are the same as I have publised at the begging of this thread. Thanks again for your intrest and help guys.