You have a 99 Monte volts light came on and you still drove then the lights flashed and everything is dead charged battery nothing new battery nothing alternator?

It is the alternator. I have a 95 Monte Carlo and this has happened to me twice in the 3 years I've had the car. Each time I had to have the alternator replaced. The first time I had a problem with the alternator I took it to a shop and had it fixed. Two years later the alternator went out again without warning. That time we took it to a different shop and bought a new alternator with a three year warranty so it'll be free if it goes out two years later again.