how come i can't open iTunes?

itunes has stopped working, i cant open it up. Ive tried restarting my computer many times and i have tried reinstalling itunes serveral times. i have tried changing the compatibal mode too but that doesnt work. i troubleshooted it and it said incompatibal application. ive looked online on how to solve this problem but nothing has worked. ive tried dowloading quicktime as well and that doesnt even open. i trobleshooted that and that says the same thing. i have a windows 7. please help