So it does not show in My Computer??
Not sure why it shows in Disk Mgt if this problem, but in your original computer it was probably the Master and yuu're now using it as a slave. The new one is probably using cable select and the new 80 conductor cable, so try setting the jumper on the old drive to cable select, and connect to the grey [gray??] connector on the Primary IDE ribbon cable.
Just a WAG.
I have a new computer with OS Windows XP Home Edition, I'm trying to install my old hard drive OS WIN 98 SE, so I can swap files, the Bios recognize , and the Disk Management of XP show the disk and says it is active and "healthy", but It does'nt show on My Pc, or any other place. What can I do??? Thanks for the Help!!

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