Once you have upgraded to windows 10, Now you can try to do a clean install without errors. There is not many things that you can do in this situation but you can always install Windows 8.1 or Windows 7 again and use the Free Upgrade Feature to get rid of Error 0xC004C003 Product key blocked. Method 2: Installing Windows 7/8 then Upgrade. Make sure you take a backup for any of your important Files before you Perform above steps to Fix code 0xC004C003 Product key blocked in Windows 10 Note: Please Understand that you will loose all the files/Folders from the drive where Windows 10 is installed. Step 5: Sit Back and wait until everything is over and see if the Error 0xC004C003 is Fixed. Watch this video to see a few steps or so. Step 4: You will see Reset this PC Option so Click on Get Started. In this video I'm going to show you how to fix a very common Windows 10 Activation Error which is Error 0xC004C003.
Step 3: Now on the left Pane you will goto Recovery. Step 1: Click on Start button, then go to Settings
Resetting your PC might just Help you to Solve this issue.This doesn't Work always but its worth the try.