I don't have water pressure. If I turn on one line I get no pressure in the other lines.What can cause this?

Is this your home or place of business? Do you have a well or are you on city water supply?

If it is your home and you are on a well, it may be your pump is failing, your water table is low to the point you do not have enough supply, yor pressure switch and expansion tank are not working correctly. I would need additional information to help you.