loss of brakes

I have new brakes all the way around vehicle but a couple of times when I went to apply brakes the pedal went right to the floor, after pumping them up it worked fine for a couple of weeks until it did it again. any help would be appreciated.

There is either air in the system or the master cylinder is failing.

Or you have a leak. Is the fluid low?

Yeah sounds the master cylinder but you definetly want to check out everything the guys posted. Brakes aren't something you want to forget about.

fluid is up and can't find any leaks, how do you check the master cyclinder

Hold down on the brake pedal does the pedal stay up or go down gradually. Your symptons sound like a master cylinder unless you did brake work recently and didn't bleed properly.
Go to a parts store and purchase a rebuilt unit. This is only if you know to bleed the brakes.
Otherwise go to a good garage and get it done. At some point you will hit the pedal and ram a police cruiser.
This will really make your day.