Change MediaBootInstall from “1″ to “0″.
Open the Start Menu again and type cmd to display a shortcut to the Command Line utility. Right-click this shortcut and choose “Run as administrator.” Handle the UAC prompt.
In the command line window, type: slmgr /rearm
Then tap ENTER, close the command line window and reboot. When Windows 7 reboots, run the Activate Windows utility, type in your product key and activate windows. It should just work.