First, (and I'm not a pro), I'd adjust the pressure tank properly. To do that, you need to shut off the pump, open a faucet to relieve pressure in the system. Then, knowing the cut-on point of the pump, adjust the pressure tank to 1-2 pounds BELOW that value. If, for example, your system should run the pump up to say 50 pounds, then shut off, a typical turn on point would be 30 pounds. In that case, the tank's pressure should be set to 28-29 pounds.
If you get any water out of the fill valve on the bladder tank, it is shot, and needs to be replaced.
If all is well there, then shut the water faucet/valve you opened to relieve the pressure in the system, and turn the pump back on while watching the system's pressure gauge. If it is working properly, it should build up pressure to the shut off point (50 pounds in my example). Then, once it is off (adjust the high point if requried), open a faucet while watching the gauge. Check to see where the pump turns back on. If it is at the desired 30 pounds, you are set. If it turns on at some other pressure than that, adjust it up or down as needed.
There should normally be about a 20 pound difference between turn-on and turn-off, and the bladder pressure should be just below the turn-on point. Hope this helps.
Note, if the pipe to the gauge and switch is filled with rust or blocked, the controls can't detect the system's pressure, and you will get erratic results. If this doesn't work, tell us what is happening, and someone else will have some thoughts.