That sucks. Tried it in any other pcs?
What does windows disc manager say?
Start>type in manage>computer management>select 'disk management' under storage and see what it says about the partitions(healthy, active etc)
Have you tried checking the disc for errors?
(go into computer>r click the drive in question>properties>tools>error checking)
Inside the shell of those things is a plain old laptop drive. Sometimes the circuitry that allows the SATA>USB interface gets affected - quite often from people who simply yank it out rather disconnect it from the USB manager (among many other reasons)
Also, just to be sure, try some different USB cables/ports if possible