External Hard drive shows up in Device Manager but not in Disk Management

My external Hard drive shows up in Device Manager but not in Disk Management. It uses a usb cable with two usb heads on the end that plugs into the computer and one end that plugs into the drive itself. After I fooled around with a usb hub with the cable (basically, I tried plugging the cables of the usb hub and the hard drive in different ways) my hard drive is not detected anymore. When I plug it into my laptop, the little bubble on the bottom right pops up and says your new hardware is ready to use but then nothing happens.
Also, there used to be two lights that lit up (one green and one red)but now only the green light lights up. Can someone please help me?