I seem to remember that there is a limit to the number of times you can plug and unplug a device under certain circumstances before it goes AWAL.

OK to find your service pack level, right click my computer, click properties, and it will tell you on the general tab.
Try uninstalling usb in safe mode, disabling it in bios, then rebooting a few times before enabling it and reinstalling in safe mode.

That little safely unplug hardware is there for a reason, yanking the plug can cause your data to scramble. Can you try this drive in a friend's machine?