Do you have a deep well (over 25') with a submersible pump or a shallow well (25' or less) with a surface pump?
What size pump? 1/2 hp? 3/4 hp? Other?
What is the cut-on/cut-off pressure set at? 20-40? 30-50? 40-60?
What is the air pressure in your pressure tank? (It should be two psi below your pump cut-on pressure with the pump off and water pressure drained down...test with a tire guage.)
You may just need to air up the pressure tank, if you changed the setting(s) on your pump pressure switch. If necessary, air it up the tank with a bicycle pump, or portable air tank or compressor.
Excellent tutorials on wells and pumps FYI: