The only thing I can think of is... Take the disk off, boil it in the sauce pan. Get some sandpaper and take the shiny layer off the pad. Rebuild it all back together. Then go ride round with brake slightly on, for about 10mins. By this time the rotor should be very hot, Then get some ice cold water and poor it over the disk. Then ride normaly and you should feel the power again. If this doesnt work the first time then try it again.