No mention of the host machine. Some require update motherboard drivers. Some find issues with Norton's scanning of removable media. You didn't reveal anything about the host machine or what software you have running at the time of the issue. In fact, the "issue" is not very clear but I'll guess the drive letter didn't show in Explorer?
I have the CHRONOS External Case Model No: HD-338-U2 with an 80 GB HD that was functioning very well since I upgraded my Windows XP PRO with the SP2.
My PC could see the External Case and the HD and in accordance with the manufacturer the Windows XP PRO have already the necessary drivers, but all my attempts to go back to the known well functioning situation were in vain.
Please for your advice how to approach this problem.