Unable To Download New Itunes/quick Time Update

Currently I have an update advisor that keeps prompting me to download new version of Itunes/Quicktime, However, each time I attempt to save there programmes they do not work as they cannot remove the old application and an error message looking for the correct path is indicated. I did recently have an issue with my laptop when it was powered off when operating, the problemn is now I have lost the orginal Itunes programme. So how do i resolve this issue? I have tried to download these programmes only, but again the same problem occurrs when I try to open up an application.