This is quite a tough one, First does the external hard drive appear when on your computer at all? I would assume disk "c:" that you mention is your main drive or your internal harddrive. If you don't see your external on the computer when you have it plugged in and turned on. Then there is a promblem. 1) Make sure driver is installed, usually when you turn on the external harddrive or plug it in to the computer, the windows sound (found device) usually pops up. 2) Check all connections if all is properly made, and if you have another computer, test it on that computer if you get another different result. If same result is made, and all connection are properly secured. Then you external harddrive enclosure, or the harddrive disk inside it is bad. 3) Listen to your harddrive to see if you hear the drive inside it spins, or if it is making any noise. If spin you could be ok, if it is humming or clicking loudly like it's stuck, then you are kind of done for and could pretty much say goodby to all those files and stuff (with exception) 4) You can take the hard disk inside the external enclosure and hook it up to a computer (if you need help how to, let me know) and see if the computer is able to read it. If not, then definitly your drive is damaged. You can still recover the files, but can't gaurentee a full recovery. In that case, you can take it to bestbuy, office depot, and tell them about the promblem and have them do a data recovery. It is costly, I mean very costly. Anywhere from $250-$750+
Now, if your computer could detect it and give it a drive letter for exmaple D:, but unable to access the files, you can probraly do a error-checking when right click for propertie of the drive.