Windows 7 upgrade doing a clean install
Microsoft doesn't really want an upgrade install to be done on a blank drive or where you wipe the drive. Why I do not know. I personally do not like doing upgrades from Windows. If I am upgrading from Windows XP or Vista, I prefer to wipe the drive completely and install fresh. This to me is the safest method. It avoids possible conflicts. However you will loose all data on the drive so you will need to back up all your personal files that you don't want to loose before doing this.
Even though Microsoft tried to make it where upgrades will not work on a blank drive, it is still possible to install Windows on a blank drive using an upgrade CD. Below is three methods to do the reinstall. Try the methods in the order I have them listed below.