External Hard drive failure

Hi, I have a Verbatim Store n' go ex hard drive which used to work perfectly with usb 3.0 and 2.0. A few weeks ago it stopped working with 2.0 and now not even with 3.0. When I plug it in the hard disk starts to rotate and lights up normally, but is never shown on the drive list. The computer doesn't even do the beep sound when a usb device is connected. I tried on 2 different pc's but they show no result.

Any kind of help is greatly appreciated