FATE.T.HARLAOWN

2 reason only..:1.power supply don have enough power
                         2.external hardisk already shock...
maybe power supply don have enough power la...because you say your external hardisk can detected before you install a new graphic card...graphic card need very high power...you know,my graphic card is nvidia9800 1gb ram,so i have to chance my power supply from 400watt to 550watt to have enough power for my pc and graphic...