Do you have windows xp ? with sp2 ?
does your Moms pc support usb v2 or v1 ?
also your usb enclosure is it usb v1 or v2 ?
does the hd boot in your laptop ? what is the OS ?
Why are you taking it out of the notebook and connecting it to your Moms pc
you might try disconnecting the usb cable , reboot then plug in the usb cale after xp has loaded fully.
try this also
go to control panel, ( classic view) , admin tools, computer management, disk management, see if the hd shows there.