Will the starter do anything? click, chatter,etc., try turning on the headlamps and turn the key as if to start vehicle.,see if the headlights dim,then if so you have a good starting connection, then more than likely the battery needs a chg, radios and lights will light seemingly o.k. but a starter needs higher current to operate and this is where it will fool you, the only other thing might be is if you left the key on too long and the alarm sensed this and cut the starter power so as not to be stolen, just an idea