Hmm
It was a Maxtor 4 touch external hard drive - a Seagate Barracuda 7200, 500Gb hard drive.
I've removed the HD from the enclosure and using a USB Hi-speed SATA connector have tried it in all our PC's.
Nada.....
I've ordered a replacement 1Tb drive and when it arrives we will "review" our back-up techniques.....
Very sad