Have you followed the information in the windows help file.
To activate Windows on the Internet The Windows Product Activation Wizard is located in System Tools. To open a system tools item, click Start, point to All Programs, point to Accessories, point to System Tools, and then click the appropriate icon., then click Activate Windows.
Follow the activation instructions that appear on your screen.
Alternatively, you can open the Windows Product Activation Wizard by clicking Start, then Run, and then typing "oobe/msoobe /a".
You can use your Internet connection to activate, or activate and register, your copy of Windows. Activation is required within 30 days of installation.
If you choose not to activate Windows now, reminders will appear periodically during the next 30 days. After that time has expired, you will be required to activate in order to continue to use Windows.
If you have not yet activated Windows XP, you can do so at any time by clicking the Windows Activation icon in the system tray to initiate activation. Once you have activated Windows XP,