Car doesn't start

Ok so yesterday i changed the transmission oil in my 03 3.2L the car has been sitting in my garage for like 3 months, when i garaged the car i took the batery out to put it in another car so yesterday when i wanted to turn on the car to fill the tranny oil !!!there was no power!!! nothing not even the dome lights, so i cheked all the fuses in the engine compartment and the ones in the back seat but all where fine, anyone has any suggestions on what happened?