If you have files on the stick and it asks for formatting, the file system is probably damaged. Try a quick format on the USB-stick. DO NOT save any files to the stick. Use a file recover tool on it, like example: Piriform's Recuva. Use the Deep Scan function.

If it says that the files are probably gone, sorry. Try using it on a different system, if it says the same thing they are definitely gone. Good luck I hope it works on a different system.