- 1). Open a Web browser and download the Windows Product Key Update Tool from the Microsoft website.
- 2). Open the Update Tool program by double-clicking its icon. Click the "Run" button when prompted.
- 3). Enter your replacement 25-character product key in the corresponding fields. Find the product key on the back of your Windows XP installation CD case.
- 4). Click "Next" to start the update process.
- 5). Close any open programs.
- 6). Click "Finish" when the "Update complete" message appears. Your computer will restart automatically.
- 7). Follow the on-screen prompts after your computer restarts to reactivate your Windows XP installation using the new product key.