Sir,
Try mo rin to...
Turn your PC off... remove the power cables from the power source... hold down the power button for 10-20 secs (discharging the static)
remove all Devices na naka connect sa PC mo like printers, scanners, speakers, etc...
make sure ang ikakabit mo lang sa PC mo eh yung power, monitor, mouse and keyboard...
Boot boot your system up (kung USB yung mouse and Keyboard mo remove mo after boot -- anyway hot pluggable naman yung USB devices; kung hindi sya USB nevermind just keep it plugged in) and plug your External HD ---check mo kung may balloon error message parin...
Pag meron parin Motherboard mo na yan sir... hindi sya USB2 compliant or hindi sya naka set sa BIOS...
Hope this helps....