If its an automatic it might not be in park if it is in park could be a senser if manual could also be a senser somethings not right with the gear box. there for not allowing it to start. Maybe the alarm system needs to be reset if you changed the battery.
Make sure that the battery cable is hooked up down at the starter , if it is you should have power at the starter, also cheeck all your fuses . There should be a fuse box under the hood and one under the dash . It sounds like you may have a bad starter .