Brakes wont stop! help ASAP

[jsuh s14]

okay. so here i am with a brake problem screweing me over. i thought i had a leaky rear right caliper, so i went out to a junkyard and bought another one. replaced it, and braking was better. still shitty but better. now.. (about 5 days later) my brakes wont work for shit. i press the pedal down ALL the way to the floor mat, and the car still takes a really long time to drop.. id say about 15-20 feet traveling at no more than 25 mph. so.. what to do? i dont see any leaks, the fluid in my resirvior isnt much lower.. so whats the problem? also, these is a "dead spot" in the early stage of braking. when i press the brakes for about 3-6 inches down, the car seems to not stop, or stop VERY slowly. Also, i have bled to brakes to a degree, but have not flushed out the entire sytem. please help me guys. thanks