Erm, I'm actually running an external hard drive as I type
and I haven't had any problems with it.
What I could suggest is try unplugging it and plugging it back in...
If not, is there a CD that came with the device? If so use that...
Other than that, I could say go to Device Manager find the item, right-click and press "Uninstall" (MAKE SURE ITS NOT YOUR HARD DRIVE INSIDE YOUR COMPUTER) then when thats done, go to Action -> Scan For Hardware Changes... and see if it detects it.