Sata sagem 320gb - Western Digital 320GB MyBook External USB 2.0 Hard Drive

You have not stated what sort of problem ?????

click start control panel administration tools computer management device manager look through all of your devices if you see a yellow question mark?or exclamation mark ! or red x
right click to reinstall drivers or

if you can see your usb but its not working
ports(com&lpt)right click update driver

sometimes the wires inside the cable will be damaged due to bending or stretching or placing heavy equipment upon the cable

just replace the cable of the hard disk, when you plugged the external disk drive you got that windows could recognize the USB device change the cable everything should work fine again,

check the USB leads that attach to the motherboard usually red-white-green-black make sure they are securely seated and have no dust build up on them dust will cause static and a lot of unforeseen problems

if this fails to fix the problem
you might have to install a usb 2 or 3 card they are cheap and easy to install you can buy these on Ebay very cheap
hope this helps