Kilometers wont show, but an error msg will!?!

Hey, I have a 2001 cavalier 4dr. I just recently had a car stereo installed, and a week later I had a dead battery for whatever reason. So I gave it a boost,and still wouldn't start. I then gave up and the next morning i decided to start it up without any boost, and of course it starts no problem. But then my remote keyless entry wont work, my gas gage doesnt read properly and where the kilometers are shown, it now says "ERROR". I thought maybe the cause of theses problems were caused by my car stereo. So i took it back to where I had it installed and the guy uninstalled the new deck, and plugged in the new one and still same problem. He checked all the fuses and they were fine. He didnt cut any wires to add the new stereo, it has its seperate harness and is powered by the windsheild wipers. I took it into the shop and they hooked up a computer reader device thingy and they couldnt determine what was wrong with it. It is under warranty and I'll be taking her in on monday. I was just curious if any of you have dealt with this problem before? Its very annoying. My kilometers no longer add up, so I could drive as much as I want and it would stay at the same number approx. 49,795 km's (very low km's i know for a 2001)

Thanks for your help

The car has to be re-coded....what you do is reinstall your stereo, sit in the car, lock the doors, turn the car to on, but dont start it...let it sit there, on, for like 10 minutes....then turn it off, take the key out, then put it back in and try to start it...you may have to do it a few times....

Hey, I dont know how to reinstall new deck. The wires that go to the fuses are disconnected and I dont know how to put them back. I tried plugging in the original factory stereo and I get a LOC message. If I have the car off, no keys in and plug in the factory one it will play no problem, just when I turn the key it gives me that LOC msg. I tried what you said with my old one and still not working. Thanks for your help though.