what would cause all power to go out?on a 2000 dodge neon.

To start with check that the car is still grounded, check the negative battery cable is well-connected to the frame and check the negative from the alternator is also grounded. Bad/corroded terminals will kill power. Also check the main relay (aka ASD aka auto shutdown relay) is still working. You should test the alternator and battery, as you could have a problem with the charging system.

My guess would be dead battery. All KenF said you should check.