Re-activating Windows 7 Product Key

When you are done, you should have nothing but unallocated space. (there should be no partitions at all) Then, clean install Windows 7 to the disk. The installer will configure your partitions for you. At a certain point in the stall, you are asked for a product key. Do NOT enter one. Further, uncheck the box to allow for automatic activation.

This first install will not have a product key until later. When it is done installing, you will have a clean, full install that you can't activate with an upgrade key. At this point, you can either: 

a) start an upgrade install of Windows 7 on top of the new install, or 
b) modify the registry and reset the license manager to let you activate the current install. 

The first method is fairly self-explanatory. After the second install, delete the Windows.OLD folder (since it's pointless), and activate using your upgrade key. This is the Microsoft approved way of doing this with an upgrade disk.

 The second requires a bit more work, but is far faster, because you don't have to sit through a second install. 

First, make sure you don't have any pending updates that require a restart. If you do, install them, reboot, and then start this procedure. 

Once your system is stable, open regedit.exe (You can search for it in the start menu) Find this key: HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Setup/OOBE/MediaBootInstall. Change the value from 1 to 0, and close the registry editor. 

Start a Command shell as Administrator (find it in the start menu, right click on it, and select "run as administrator") You will need to authorize the UAC. 

Run the following command "slmgr /rearm" and wait for the command to complete. (you will be prompted) 

Restart the machine, and head over the the About page. You will be notified that you have 30 days to activate, and near that is a blue link to enter a new key. Click it, enter your upgrade key, and let it activate. If all went well, you should be good to go.