1996 saab 900s brake pedal all the way tofloor
 

Hi everyone so yesterday I decided to change my rear brakes. I replaced the brakes and did not realize the brake fluid leaking out of the caliper while it was open and my brake fluid tank went empty in the front. Needless to say once everything was put back the pedal was very musshy and sponge like. so I decided i have to bleed the air out. i filled the tank with fluid, and opened the bleeder valve inthe passenger rear bleed screw on the caliper, and had my friend depress the brake. when i tightned the bleeder screw, i told him to let off the pedal he did and.. then the pedal would not come up anymore it was stuck near the floor of the carpet. since then i've tried to bleed all the 4 caliper bleed screws. two are successful, the passenger front adn driver rear no fluid comes out once the pedal is depressed? What could be the problem? oh and the pedal is not returning back to position it is still at the floor. and i checked for leaks there are none. What should i do i have no brakes. thanks in advance for your help.