The bios of whatever computer must detect the hard drive inside the external enclosure.
That requires that
- the USB cable that connects the external enclosure to a USB port connected to the computer is adequate
- the USB port built into, or connected to a header on, the computer's mboard can actually supply 500ma and is otherwise able to work with the external drive enclosure properly
If the computer's bios DOES detect the hard drive inside the external enclosure properly, at the very least,
- the external enclosure's circuits should show up as being detected by there being an entry for a USB Mass storage device in Device Manager - USB controllers for the external enclosure
....and there should also be ( but there may NOT be if data is damaged on the hard drive or if the hard drive is defective)
- an entry for the hard drive model that's inside the external enclosure in Device Manager - Disk drives
e.g. for an external enclosure of mine that has an EIDE hard drive - Toshiba MK8025GAS USB device (the hard drive model is Toshiba MK8025GAS)
- the hard drive that's inside the external enclosure should show up in Disk Management
(Control Panel - Classic View - Administrative Tools - Computer Management - Disk Management)
If the hard drive inside the external enclosure DOES show up in Device Manager - Disk drives, and in Disk Management,
- if there is no drive letter or letters for the partition or partitions on the hard drive in My Computer or Windows Explorer
- OR - if Disk Management shows the space on the hard drive as "RAW" (unallocated) when you know it had your personal data on it previously, or when you know you could see it's partition(s) in My Computer or Windows Explorer previously,
- OR - if there IS a drive letter or letters for the partition or partitions on the hard drive in My Computer or Windows Explorer, but when you click on that or those drive letters, Windows "thinks" the drive partition is not formatted
...then data on the hard drive has been damaged.
There are several programs that you could try that will probably fix your problem.
Specifically, links to some programs that can repair the data damage are here -
see response 2:
That post also has info about testing the external enclosure's hard drive. Apparently, the Windows version of Seagate's SeaTools can test any hard drive brand when it's in an external enclosure.
Do the long test.