Cadillac Repair: 2000 Cadillac Deville LHS, key fobs, battery cables

Question
My mother recently gave my 16 year old son this car. We have driven it for two weeks. Today, the traction light and the security light and a security message appeared, and the radio stopped working. I parked the car, and turned the ignition off. The doors would not unlock automatically, using the button on the door, or the key fob. The key fob would not work at all. A few minutes later everything turned to normal. Then tonight, the same problem but now the car won't start, no interior lights except the dash. We have two key fobs, neither works.

Answer
You need to check for battery corrosion at the battery cables and at the starter battery post. When you say the car won't start, Do you mean that you turn the key and NOTHING happens or does the engine crank over but just will not start ?.

Check for headlights, brake lights, horn and every electrical device and see what works and what does not.