Remember that a drive can fail at any time, so the fact that it was working fine until now really means nothing. What I have found is that the Cable that connects the drive to the PC is really **** so I would start by replacing the cable. Also, if you have another PC (friends PC will also do) plug the drive into another PC and make sure that the problem is not possibly the PC itself and not the Hard Drive. Also try different USB ports - lastly - i have found that many times it is the casing that packs up and not the drive itself - some casings can be opened and you can remove the hard drive - you can then purchase a generic hard drive case and install the drive into the new case and it will work again. Some of the new Western Digital drives though cannot be installed into a new casing as the USB port is part of the drive and cannot be removed. Like I said - first check if the drive works on another machine - if so - its not the drive but the PC - if it does not - check the cable. You could of course also have destroyed the data on the the hard drive if u unplugged it while it was stil being written to - in which case the File allocation table is damaged and you will need to re-format the drive.

Good luck