Check first to make sure that you are getting power at the pump.  When we bought ours, there was a breaker at the panel and a fuse hidden in line near the pump.  Sometimes a well-meaning previous owner leaves you little gifts like that.  When you say the breaker is good, I assume you've checked that there's power at the load side when turned on?  Also, see if you can locate the negative lead and ensure it's properly landed at the terminal strip.  If there's a plug or crimp connection near the pump, make sure it's not corroded (and for sure not made up with wire nuts!)  Once you're sure you have power to it, feel of the pump body to see if it is "humming" at all.  It's possible that either the fluid end or the pressure switch is faulty if you are getting power to the pump.  Depending on the model, it may be repairable, but depending on the age, replacement may be the best option.

I wouldn't pressurize the tank as they are plastic and you could do damage which is difficult or impossible to repair, but do make sure your tank vent (possibly a little chrome fitting in the cockpit) is free to breathe.  The pump should be able to pull water from the tanks without pressure (we've inadvertently pumped ours dry several times and had no issue getting the pump re-primed).  Also, make sure your suction strainer (hopefully you have one, ours is difficult to see just under the outboard dinette seat) is clean.

These kinds of things are where you get to know your boat better!  Enjoy the process and trace the system from end to end!

as Dan said you definetly don't want to pressurize the tanks -- they will likely split open if you apply more than a pound or two.  Your pump is located just forward of the water heater, which is located under the dry-food-storage locker (to left of the sink).  You access this area with the small square hatch board that is under the dinette seat.   These pumps do occasionally fail - but make sure you have power, and free flowing water at the inlet to the pump.  Depending on year you may have a manafold valve (under the stove or?? mine doesn't have this.  If you do  make sure these are open for the tank   you want to pull from.

if you still have problems - post back here with what you find.

best wishes
 

I had a similar problem. It turns out that someone had replaced the pump and used crimp wire connectors - but neglected to crimp them. They were held in place with tape and they were hard to see. The wire had worked itself out.
With my fantastic electrical knowledge, it was not hard to locate the problem.