Bad Pressure Tank?

I have a 100 ft well away from house with 42 gallon pressure tank in my crawl space. When water is in use the pressure gage will move quickly and continously from 30 to 60 - back and forth. When you shut off the water this stops and it reads 30. Yesterday I lost all water. I replaced the 30/50 pressure switch and water came back on. However, the same reading is happening on the gage when the water is in use - 30 to 60 back and forth. I tried the adjust the pressure switch. I has slowed down the gage a bit. It now bursts 30 to 60 every few seconds when water is turned on. With the water off it reads 38.

I shut off power to the pump and opened the faucets to drain water so I could check the pressure in the tank through the Schrader valve. I am getting no pressure reading from the tank. No water comes out either through the valve.
Does this mean my tank is shot or can I still add air back into the tank?
Any help would be appreciated.

 

Once the tank is completely drained, set the precharge at 28 psi (2 psi less than pump cutin pressure). Pressure the system back up and give it a try. If it seems to work ok, wait a few days, drain the tank again and recheck the precharge. If it's still the same you'll be ok. If not, you'll need a new tank.
Ron

 

42 gallon tank might not have a bladder. You might just need to pump air into the tank.

 

We added air to the tank to 28 psi. Gauge is reading good. No more erratic movement. Good water pressure. So far so good. Hoping it stays this way.
Thanks for your help!