You need the Windows XP serial number to update Windows.
If you purchased a pirated copy of Windows XP by accident, you will not be able to run any Windows updates. As you need to keep Windows up to date for security purposes, you can change the Windows serial number to a valid number. First, you have to deactivate Windows XP, then activate it by entering in the new serial number.
Instructions
1. Click "Start," then click "Run." Type "regedit" in the Open box and click "OK."
2. Navigate to "HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\Current Version\WPAEvents" on the left side.
3. Right-click "OOBETimer" on the right side and click "Modify." Change at least one digit of the value to deactivate Windows. Close the Windows Registry Editor window by clicking the "X" on the top-right corner.
4. Click "Start" and then click "Run." Type "%systemroot%\system32\oobe\msoobe.exe /a" in the Open box and click "OK."
5. Click "Yes, I want to telephone a customer service representative to activate Windows" and click "Next." Click "Change Product Key," enter the valid serial number for Windows XP and then click "Update."
6. Close the window by clicking the "X" in the top-right corner when finished.
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