2000 cavalier

we have a 2000 cavalier and after replacing the battery, the car will start but as soon as we push on the brake it will die. Could it be the security system and if so how do we fix the problem? We have been turning on the ignition and leaving on for a while and then trying tostart. also dies when we turn on headlights. Please help.

If it starts and idles, not the security. Double check all your battery cables. Especially the ground cable. Both ends...