01 Deville Starting/Stalling Problems

My grandparents have an 01 Deville with approx 70k miles. For about the past year the car has had and intermittent starting problem. Sometimes when you try to start the car it is like there is not even a battery in the car at all, no lights inside or out, nothing, then after a few minutes it will start, other times everything works fine but it will not turn over then after turning it off for a few minutes and then back on starts fine. Cadillac dealer cannot diagnose the problem, say that it will have to happen while at the dealership for them to diagnose it. We originally thought it may be the battery, after it finally bit the dust and was replaced everything was fine for a about a month, then back to the starting problem.

Now over the past couple of days the car has started dying while driving for no reason. The car loses all power, engine shuts off, then car comes back on as if the key were just turned to the "ON" position before starting, engine starts back, presumably from it still being in gear, doors lock and something like "attempted theft" flashes then everything returns to normal. This happened 3 times today, also the factory alarm has gone off twice with no one around the car in the past few days, and once when they were getting out of the car after parking at a store.

Any ideas on whats up with this thing would be GREATLY appreciated seeing as how the dealership is going to want an arm and a leg to diagnose an electrical issue.

Thanks in advance for all your help guys.

Intermittent electrical problems are hard to find thats why sometime it costs so much. Someplace between the battery and the ignition switch it is becoming disconnected. Check each connection. Pull it apart and clean it. A wiring diagram would be helpfull.

I'd check the ignition switch. I had a similar problem on my 2000 STS and it was the ignition switch. Does the key get hot when driving?

We found the #2 set of keys that came with the car and tried using those, so far it seems to be better, however the alarm still randomly goes off at times for no reason but as far as the stalling problem it hasn't happened again. Possibly the chip in the #1 key? Still puzzled as to the alarm issue though. Any thoughts?

Thanks for the tips everyone