If this is a IDE hdd with a Windows operating system installed on it, and it has been placed in another computer as a Master hdd, the chances of the operating system failing is high. Different motherboards have different chipsets, and the operating system recognizes IDs of these chipsets. If a hdd with a Windows operating system is moved to a computer with different chipset the operating system becomes "confused" and may not even boot.
If you have a hdd with a Windows operating system that you wish to retrieve information from, an IDE hdd that is, you need to install it in another computer as a Slave drive, and change the jumper on the rear of the hdd to reflect this.
If you have tried to use this hdd in another computer without doing as suggested, there is a chance that you can do a repair installation and not lose your data. No promises though.
Edited to add more information:When you take a hdd with a Windows OS installed on it that you have been using on one computer and then install it as a master in another computer you are asking for major problems. The excerpt below is from a Intel article which describes in detail what happens. The article also mentions a reference to an article by Microsoft, it can be seen here ."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."Alternatively, the method below can be tried, but I would back up all of your important files to removable media like CDs, DVDs, Flash drives, or a second hdd
Edited by dc3, 18 September 2010 - 08:43 PM.