I suppose you have well water, I also have well water, any how to pressurize the tank, you will find a valve stem like on a car wheel on your tank, I pressurize mine @ 28 psi.
How Do I Re-pressurize A Water Tank?
It sounds like you need to reprime the well also! If your pump is submersible then you won't need to prime it. If your pump is above ground then give me a shout and I will help!!