big problem

hi i'm scott,2 days ago my well pump started running continuosly for 3 hours before i shut it down.i have full pressure water when pump is on but my tank doesnt fill.i replaced the nozzles and the pressure switch seems to be working fine.my tank has pressure 50lbs.I dug up my well and noticed a rather big sinkhole around the pipe.any suggestions or ideas would be appreciated.i have a jet pump(sears) that when pumping goes to 80 psi.

You replaced what nozzles? Deep well or shallow well jet pump, two pipes to well or just one? Is there a check valve at the pump? What size is the well casing?

Sink holes usually mean a water leak, did you find water or wet ground?