In BIOS Setup of your new machine, check the SATA Port Mode setting near where you Enable the ports. Your choices usually are IDE (or PATA) Emulation, Native SATA, AHCI, and / or RAID. Since you are using Win XP already installed on an older HDD, you MUST set this to the IDE (or PATA) Emulation mode. In all its forms, Win XP does not now how to use AHCI devices without a driver. For a boot disk, the driver would have had to be installed from a floppy disk when XP was first installed on the HDD, and I bet that was not done. So setting to this option has the BIOS intervene and make the actual SATA disk appear to Win XP as a simpler IDE device it fully understands and can use immediately.