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I'm using Windows 7 Ultimate. I want to have Windows XP installed on my HP Compaq NC6400 laptop but this is the error it gives to me:

stop: C0000221 unknown Hard Error

\systemroot\system32\ntdll.dll

What does it mean? How can I fix it?

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Are you dual booting or is this a new installation? – Shinrai Aug 11 '10 at 14:59
up vote 1 down vote accepted

According to the Knowledge Base Article, that stop-code has two meanings:

  • The specified file is corrupted
  • An installed driver is incompatible with the hardware

So, did you install any drivers? If yes, then you might wanna try the drivers which are listed in this blog, a reinstallation might be required. If you didn't install anything and this appeared at the first boot, then you've got a problem. Try to get a hold of an Windows XP SP3 CD and try again.

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