DON'T WASTE YOUR TIME TYPING IN RANDOM NUMBERS!!!!!! My battery died and I had to do a whole lot of searching the web to find out an easier way than typing in random numbers!
There should be a plastic card similar to a credit card with your owners manual packet. It will have a 4 digit code number on it. There is a slot at dash level in the driver's side door. turn the ignition to the position where your dash lights come on and turn on the radio. Insert the card into the slot and, using the numbers on the radio, punch in the card code number. (I don't understand the whole, putting the card in the slot, just typing in your number listed on there works just fine) Radio should come back to life. If no card can be found, contact a Chevy dealer fo a replacement card.
This card saved me hours of trying to figure out what number I had to use to unlock my radio!