Any chance you're behind on Microsoft Windows updates? Check if you have all the latest updates and if not, install them.
Also make sure you're downloading the latest version. You can get that version HERE.
You say you have had Itunes installed before, make sure you COMPLETELY uninstall and remove everything related to Itunes before trying to re-install it. Sometimes leftovers from a previous installation can be the cause of this problem.
Also check if there's conflicting software that may prevent the installation, but this is usually not the case. My bet is on one of the above options.
Hope this helps.