ITunes help

Help greatrly appreciated..

Everytime i try and open my itunes it is saying the file is corrupted, so i deleted it to try and then upload a new uncorrupted file but when i try and upload a new itunes it is saying one already exists on my computer....

Can anyone advise me on to resolve this, this all started as when i wanted to sink my iphone to my itunes for some reason it was wanting to replace my info on my iphone with that with my ipad, which is not what i want, something else i cannot resolve...

Thanks for any help...