Cant install Arduino software

Hi, i had Arduino running on my laptop, Windows 7. I was messing around trying to remove a previous user and i messed up the settings so i had to get my friend to fix something in the registary. The laptop is working now but Arduino is the only software that will not run.i have done a clean uninstall and tried to re install but it just will not allow me to install. The install software option is greyed out. Any help would be gladly appreciated