I might be overlooking something, but ....
I bought an external cradle to sort out my nieces laptop (problems with virus and booting etc), I plugged the harddrive into it and then into my computer and it read it fine, removed the virus' and malware etc, put it back in hers and got it up and running.
Then my other niece asked if I could recover her college work off hers as that had gone kerput... which again it did no problem.
Then at a later date I got a new hardrive to use as a backup... it knows its there, tells me usb connection etc... but then won't see it.. doesn't come up showing as a listed drive. I've uninstalled the drivers/usb for it all, it reinstalls them when I plug it back in, but still won't give it a drive letter and make it visible ?