Why has my pen drive stopped working?

When I plug my pen drive into the usb a bubble message comes up saying that the computer does not recognise the device and that windows doesn’t recognise the problem. The red light that usually shows when it is plugged in flashes very faintly, when message appears, then isn’t there any more. HELP! Although I have most of my work backed up there are things on it that haven’t been as I was at work on my laptop and about to save- 2 hours work GONE! I know it’s a lesson learned to keep saving in 2 places but useful answers would be appreciated.