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You have to re-install Windows on to it when you put it into a different PC. Windows XP just will not tolerate being moved out of one system into another. For one thing all the hardware is now different so the disk will be full of a whole bunch of wrong device drivers which itself would cause
XP to choke, but the major reason is the plain reality you can't do that with XP. Unlike earlier versions of Windows it just doesn't like it.
There's another consideration even if you did manage to get it to work. If the PC that hard disk came out of had XP pre-installed on it when new, it's an "OEM" version (not a retail boxed version) and OEM versions cannot legally be installed on any other PC. That OEM version is "tied" to the original PC for life. When the PC "dies" that version of XP dies with it. That's Microsoft's licence conditions. So if you want to put XP on another PC when the first one has died, you have to buy a new retail copy and install that.
Edited by pip22, 29 April 2008 - 12:44 AM.