Hard Drive not working with VirtualBox on Mac OS X 10.10.2
Windows 7 does not natively support USB 3.0, which is what the Seagate® Expansion Desktop 1TB USB Drive - Specs interface is.  To work around this Windows 7 native limitation, if no USB 3.0 3rd party driver for this device is available, you should be able to get it work by either plugging it into a USB 2.0 Port or into a USB 2.0 Hub before attaching it to the virtual machine.