My WD External hard drive not recognised

Hope someone can help. I have a 1T WD external drive on which I backed up all my files and in particular photograghs before leaving to live and work out in the Persian Gulf.

I had successfully accessed teh drive using my laptop on one day only to find the following day, the power unit had failed.

I replaced the power unit from an official source paying the premium and the HD powers up, spins and the blue light showing activity at the data plug is evident however the laptop and my pc at work dont recognise the existence of the HD.

I have tried alternate cables but to no effect. 

No known maltreatment of the HD and as it survived the transport in my camera bag on the aircraft from the UK, and worked, assume there was no effect there.

Any ideas what to do next?

Regards

Graeme