Is the pressure good after pumping up the tank?
If so, it sounds to me like the next thing to check is the pressure switch. If it is adjusted incorrectly the pump will keep running as it is trying to reach a pressure to high for the pump to achieve.
Do like Bill said and google the instructions for the d square ( I believe) switch. It is not that difficult to properly adjust. If you read the instructions multiple times you should be able to do it. I think there are also some good YouTube videos on how to do it.
Good luck and report back.
All the Best,
S/V Rita Kathryn SM #466
Currently Cruising Bahamas