Thank you for your response. It should still be under warranty, but I am wary of sharing my information with the shop I bought it from - data protection and all that. There is nothing dodgy on it that I wouldn't share with someone I trust, but don't like the idea of handing over information to complete strangers!
It has only just stopped working, when I plug it in, the blue light comes on briefly and then goes out. The laptop does not recognise that it is connected. The device makes a low 'humming' sound, like it is working, even though the light is not on. I have always ejected it properly, but when I go to eject it now before unplugging, it no longer shows up. Just very frustrated.