You cannot activate Windows and when trying to Activate Windows do you get the following error.

"A Problem occured when Windows tried to activate. Error Code 0x8007007B."

Cause

• A KMS Key has been used when a MAK Key should of been used
• The activation state has become corrupt or has been changed a state that cannot be activated.
• This can also occur is a pirated version of windows is used and the activation technologies fail. There is an activation status of 'Pirated Windows' and once this is set even if windows is running you can never activate it.

Solution

1. Reset / Re-Arm the activation status. I used a utility called 'Windows 7 Loader Extreme Edition v3" which allowed me to reset the activation status and then i could used the correct MAK Key
2. Reboot the computer

3. Change the product key to an MAK (if required). To do this, follow these steps:

   1. Click Start, click All Programs, click Accessories, and then right-click Command Prompt.
   2. Click Run as administrator. If you are prompted for an administrator password or for confirmation, type the password or provide confirmation.
   3. At the command prompt, type the following command, and then press Enter:
      slmgr -ipk xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
       
      Note In this command, the placeholder xxxxx-xxxxx-xxxxx-xxxxx-xxxxx represents your MAK product key.
4. reboot the computer and the activation status should now be correct with a valid key if entered in previous steps.

Other Resources

• Download MGA Diagnostic Tool (Microsoft Genuine Advantage)
• Microsoft Genuine Advantage Diagnostic Tool - Description on thewindowsclub.com
• Error 0x8007232b or 0x8007007B occurs when you try to activate Windows -  other solutions from microsoft
• windows 7 error can't activate 0x8007007B - Microsoft Community - Mentions the use of "slmgr.vbs /ato to activate and update KMS client information"