it may be the hard drive broken or the enclosure.

New USB enclosures are about £10 on ebay, USB3 is fastest (and backwards compatible)

I have lots of external hard drives with various old backups.

I dont bother with software to backup,
just use windows to open two file windows and copy across into a new folder on external hard drive (or to an old folder if I want it just to overwrite files which i've changed since last time.

I agree with Oliver, I have a C: windows partition and a D: data partition which holds my documents and most of my other data folders, and my thunderbird email folders.