Earlier today in the office I was copying a 4GB folder from a laptop to an external harddrive. It is one of those USB 500GB drives that are very common nowadays. The problem was when I finished copying the files/folder (or maybe it was not finished) when we plugged its USB into a PC the drive was detected but the files are missing. It also says that there is something wrong with the drive and it needs to be reformatted.
A few weeks ago my girlfriend also had the same problem in their office, although a different media, since what they had was a 32GB USB thumb drive (the smaller ones). The issue was the same, the folders and files can no longer be accessed or viewed in Explorer in Windows or even Finder in a Mac.
My colleague who owned the harddrive said that it is fine, we can reformat it, but I did not want to. I do not want to succumb to machines! Men are still mightier than the ones and zeroes, 
) although i admit this post would not have been possible without a PC/Mac.
I plugged the USB harddrive in my work PC, luckily it was detected, so that is good news. The only problem is the files / folders were missing, and yes the prompt to format it was there. Here’s how I recovered the files.
1.) Plug the USB HD
2.) Open “My Computer”
3.) If the drive is detected it is a good sign. If not, try waiting for a while, something should pop up on the system tray (commonly found on the lower right of your screen with the other small icons as well as the clock – in standard layout)
4.) While on the My Computer window, Right-click on the harddrive.
5.) Choose the last option – Properties
6.) From the Properties, choose Tools
7.) You should now see the CheckDisk along with Defragment, and Backup.
8.) Click the “Check Now” button
9.) You will be prompted with 2 checkboxes. Check both, it should be fine.
10.) Then wait for it to finish. In my case it was Phase1-3 of checking went on swiftly, and Phase 4 was quite a wait, so be very patient.
That’s it! After the checking was finished, it did not even prompt, I just checked the drive and there I found the files recovered.
I forgot to mention that I am using Windows XP. Here’s a link from The How To Geek on how to do it in Windows 7 / Vista – here
