1999 Nissan Sentra Brake Issue

Brakes seemed to be not stopping car as quick and right front brake would smell like its hot. Changed brake pads and rotors (rotors were very worn, pads were still good. But changed them anyway). Now have no pedal pressure. Have bleed all four brakes both with the engine running, and with it not but with the key on. Can build up presure with key on and engine not running, but as soon as start the engine pedal sinks to floor. When pumping pedal, engine seems to die down. Not sure if that is relevant. Have checked all lines, have found no leaks. Thinking of changing master cylinder, but not sure if that is the issue. What could the problem be. Brakes did work fine before changing rotors and pads other than what I stated before. Please help.