Different things happen on different versions of Windows when activation fails or when you exceed the grace period without performing Windows Activation.
Important: I highly recommend that you back up the registry keys you're changing in these steps as an extra precaution.
If you're uncomfortable making registry changes in order to change your Windows XP product key, using the popular free product key finder program called Winkeyfinder is another option.
The OEM Activation feature helps ensure that most people will never have to deal with Windows activation.
PC manufacturers insert a digital product key into a Windows PC’s BIOS during manufacturing.
Microsoft Office also includes an activation feature that requires you activate new copies of Microsoft Office with Microsoft to protect against piracy.