Sounds like the tank is shot (I fully agree with the others). Turn the power off to the pump. Verify you have pressure on the gauge. Open a faucet. If it immediately drops to zero, that is verification. Now it is (unlikely but possible) that you just lost air pressure, but the bladder is probably gone, so it is new tank time. If you get water out of the Schrader valve on the tank, then that just is another confirmation of a shot tank.
Now, it is possible that you don't have a bladder tank. Then, you may have a problem with the air admittance valve (did I get that name right?). But, they are not as common as bladder tanks anymore.