i dropped my hd today at work, and it stopped working. Giving it a squeeze (!) around the outside of the case has brought it back to life, as has propping it up at an angle - long enough to back up my work anyway.
By the way, the problem i had at first was not enough power to my usb drive - it runs off a laptop, and for it to run, I need to plug the usb lead into the usb drive - AND - another end into the monitor port on my laptop - i presume it is a a power problem. This is the only reason I can think of...
However on other laptops and all PCs I don't need to worry about plugging the monitor port in - there is obviously enough power to run the drive by itself.
Hope that helps