You need to find out if your electric heating element is OK or not. Most likely, it's dead.
If you drained your water heater (empty), and then hit the electric (on) switch, for even a few seconds, it will burn up the heating element immediately. It has to have water around it, otherwise, they burn up. Same is true in your home electric water heater (top and bottom elements).
My camper came with two switches. The one inside the camper on the wall and the one at the water heater. Both have to be in the ON position for them to work. Considering I leave my camper plugged in all the time, I always flip the rocker switch at the heater to off. Then if the switch on the inside gets flipped, it will not come on and risk the element burning out.
More than likely, it's your heater element. Its an easy fix to swap them out.