Itunes HELP

Hey so im trying to download itunes 8.0.2 on my windows pc and everytime i try it always stops and says something about having an error writing to file mobile device service and i dont use itunes for a phone. ive had itunes before but something happened with it so i uninstalled it. ive been trying to install it for like 3 days already! so i really need help bcuz i got a new ipod but i cant put music in it cuz it doesnt want to download! can someone please help me. oh and the only thing thats downloaded is the quick time player