Macromedia flash 2004 mx programming game problem?

i have programmed a space shooter for my coursework at uni, and for some reason it wont let me add any more working code to it if i do it just runs as flashing background, then if i even remove what i just added its still broke, so far got ship shooting down randomly coming asteroids and score counter, but i cant do things like intro screen or game over or even my ship dying if it gets hit, which i know how to do but anything i put in makes a flashy game lol that is broke, anyone know what it could be?