My external hard drive continues to be unrecognised, despite me trying a number of options including shutting-unplugging restarting my laptop (after removing battery too), disc management, driver unstall-reinstall, etc. the moment I plug in the external hard drive, a persistent green light lights up on it, and a pop-up window says "unrecognised usb device" (unknown device on device manager)...clicking on computer icon does not show anything! Have so many important documents & certificates there..please help!