I have a Sony 64Gb flash memory stick, but recently have found that after transferring folders containing zip or rar files from my laptop to the stick, the folders or individual files on the memory stick are showing empty. The system records that the appropriate space has been used on the flash memory, but there's nothing showing up. Could this be a hardware problem, a driver problem or somehting else? I've tried disk checks and reformatting but the problem is still there