Agree you may have a leak, check that out first. Is it pumping water to faucets? If so then the pressure sensor is maybe bad. If its not pumping AND you have water then the pump could be bad. Now changing the pump(and this depends on how EZ it is to get to) is a simple process. Turn water to pump off, unhook electrical leads, Unscrew inlet and outlet from pump, unbolt pump from mounting, reverse to install. You didn't say what pump you have but there are dirrect replacements.
LEN