Hi Richard,
Windows file explorer
Delete the following folder (where <Windows userid> represents the name of your user account on the computer).
C:\Users\<Windows userid>\AppData\Local\Alibre Design
NOTE: the AppData folder is hidden by default in Windows, you may have to turn on Hidden Items on the View tab of File Explorer.
After deleting the folder contents, re-boot the computer then launch Alibre Design.
You should be prompted for registration information (note you will need your activation code).