Disconnecting the battery is not a good idea on newer cars. In particular, GM, BMW, and Volkswagen have designed in a number of tricks that require trips to the dealer to have multiple computers unlocked.
First check all the fuses under the hood and inside the car. They often blow from the surge of reconnecting the battery. Also try unlocking the doors with the key. If that works, it was in theft mode. As I recall, it will still crank in theft mode; it just won't run, but regardless, see if the "Security" light on the dash is on or flashing.