My external Seagate 500GB expansion drive not working!

http://www.dabs.com/products/seagate-500gb-expansion-de...
That is the exact product.
It was working absolutely perfectly. Then I reformatted my PC and now it just won't work at all. When I first plugged the hard drive in, it did install the drivers and it said that it was ready for use. But when I go into Computer, it's not there (I use Windows 7 x64). I've tried various methods such as Computer < Right Click < Manage < Disk Management, but this method did not work, the hard drive did not show. I've tried uninstalling the driver, then restarting and reinstalling the drivers and that didn't work either. I've noticed that when I plug the USB in, it doesn't show that the USB is plugged in the icon in the corner of the task bar.
Please help. It was working perfectly remember, so I highly doubt it's broken.