Don't you hate it when you replace a hard drive, install a perfectly legal copy of Windows 7 Upgrade and then try to activate it and it says it can't be activated because it is a clean install? Here's a fix that worked for me:
- Make sure there are no pending updates
- Change HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionSetupOOBE MediaBootInstall from 1 to 0
- In an elevated administrator command prompt type slmgr -rearm
- Run Activate Windows and use your key!
Found it here. Thanks mydigitallife.info!