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Moving a hard drive with Windows* 2000 or Windows XP* already installed to a new motherboard without reinstalling the operating system is not recommended.
If a hard drive is moved to a new computer, the registry entries and drivers for the mass storage controller hardware on the new motherboard are not installed in Windows for the new computer and you may not be able to start Windows. This is documented in Microsoft's* knowledge base article †. This is true even if you move the hard drive to a motherboard with the same chipset, as different hardware revisions can cause this issue as well.
Additionally, moving a hard drive to a new motherboard may not exhibit any errors until you install new IDE drivers. This is because each chipset uses a different Plug-n-Play (PNP) ID to identify it. If you move your motherboard, your registry will have multiple PNP IDs (for the old hardware as well as the new hardware). If there are multiple entries in the registry, Windows cannot determine which hardware to initialize and therefore fails with a STOP error.
You could try doing a repair installation of the XP, you might get lucky.