It sounds like the files are still on the flash drive.. My question is whether you have the appropriate program to open those files on the computer you're using? If you've copied the files from one computer to your flash drive and are then attempting to open them on a different computer, does the second computer have the associated program installed so it can open the file.

Either way, please give us more information about the type of files, the operating systems involved, and most importantly, where are the backups to these two files?

Hope this helps and let us know more.