USB devices disabled error

help! i am trying to transfer my pics from my camera to my mac OS X with my usb cord. My error states device using too much power... the only reason I am trying this method instead of my SD card is ... I have already loaded the pics into iPhoto, BUT some of them only loaded 1/2 way for some weird reason. they are 1/2 blacked out. I tried reloading. but it says "already imported" UGH I want all my pics on the computer from my vacation. help. thanks in advance.