One possibility is in the way that the several computers have their SATA port modes set in their respective BIOS Setup screens, combined with which versions of Windows are installed. Windows XP does not know how to deal with drives set as native SATA or AHCI devices, whereas Vista and Win 7 do handle them right away. If that is your situation, there are two easy solutions for the system that is using XP. One is to go into the BIOS Setup screens and change the SATA port configuration for that drive to IDE (or PATA) Emulation so XP will be fooled into thinking it is a simpler IDE device it can use. IF you are not trying to boot from this particular dive, the other option is simply to go into Win XP on that unit and install on it the proper device driver (for a SATA or AHCI unit) that corresponds to how the SATA port mode is set.