First go to Windows Update and install any critical or important updates. Uninstall any antivirus, antispyware and firewall programs which may be present on your computer. Go to
http://onecare.live.com/standard/en-us/install/install.htm sign in using the Live ID and password used to purchase One Care and begin the installation. If you encounter any issues downloading or installing One Care please post back with the details of the issue and any error messages you may see.