If the pressure gauge does not move or is in question, replace the gauge. Next, turn off the well at the electrical breaker and drain water out of the plumbing. You cannot properly check the system with water in the pressure tank.
Using a tire pressure gauge, test the air pressure at the air (Schrader) valve, which is often on top of the pressure tank. This should read at 2-4 psi less than the turn on pressure of the pump. Example: if the well system runs between 40 psi and 60 psi – the turn on pressure is 40 psi and therefore the air pressure should be 38 psi.
Next, add air through the use of an air pump or remove air as needed to achieve the 2 psi less than the turn on pressure.
Lastly close all faucets and turn the electrical breaker back on and check for leaks.