Lost my back up information

Hello,

I backed all of the documents on my computer up onto a flash drive then set my computer back to the factory settings. When I tried to restore the information from my flash drive back on to the computer it was there anymore. After I did the back up I made sure that the files were there on the flash. When I tried to recover them they were no longer available. Under properties the backup file says it is 3.47 gigs, but in the recovery mode it says that there are no files available. What is wrong