i get a please insert a game disk , when i have a disk in my drive. help

yeah i went out and bought house of the dead 2 for dc , and tried useing it , because my iso of RECV wasnt working, i got that input error crap, so i figured id try a disk game , not an iso. and now i start it up and i go to play , and it says i need to put a game in. i dont get it , help please? or contact me on AIM>> Th1CkMcRunFa5t