Tell the group more about your computer, OS, SP, RAM, internal HDD's, external HDD's how they are connected USB, Firewire, eSata, etc. That way everyone can be thinking about the same problem and come up with a good solution.
Two generic things to do in the interim.
First go to Windows Update and write down what the updates were, and KB number, that were downloaded and installed just before this problem occurred. Later, if necessary they can be uninstalled.
Other thinkg to try is to shutdown, unplug your external HDD and reboot. See if a flash drive with data on it works on the port the external HDD was connected to. Then shutdown again, reconnect the external HDD, and reboot to see if it is recognized in the Device manager, if there is a yellow warning icon or red problem icon there, and also if it is present in Disk Management. Check there to see if it is a Basic Drive, Online, Healthy (Active) NTFS.
That should get you some of the info needed or may even get you going again