Diagnosing this is almost impossible, because of incompatible device drivers. I suggest keep one disk for booting your old machine, and another disk for booting your new machine. If you need to move a BOOT disk from one computer to another, rather reformat it, and re-install the OS. If you do NOT boot off a drive, it will be readable on either machine. It is just because you are trying to boot the OS that you are having a problem. I suggest buy a new disk drive for the new machine, and install the OS on it. Then, plug the old drive onto the new machine, and copy over whatever you want to keep.