brakes problem

I have this problem with my brakes where when the brakes are pressed they make a hissing noise. They are also very weak. Any ideas?

STOP DRIVING IT!!!!!!!! i will guarantee you have a leak somewhere, check your fluid level, it should be low. if it is, check all your brake lines, brake fittings, brake cyinders. if its not, then check your pads, front and rear, and check your rotors with a micrometer to see if they are within spec. if your rotors are worn down, you have excess caliper travel and you will put too much stress on your brake system, and will cause major damage. thats my best guess off the top of my head, but like i said, whenever it comes to brake problems, do not drive the car till you find out what the problem is.