Have you tried activating by telephone? Sometimes that will solve the problem.
Here are some steps:
Activate Windows 7 manually:
1. Click Start.
2. In the Search box type slui.exe 4
2. Press ENTER on your Keyboard
3. Select your Country.
4. Select the Phone Activation option, and hold on for a real person.
Mike Corkery, MCT, MVP (Office Systems), MCSD (Windows Store Apps), MCITP, MCPD, MSF, etc. Please do not forget to click “Vote as Helpful” if any post helps you and "Mark as Answer”if it solves the issue.