I have a 1gb flash drive which is used as a backup of selected folders. I use Cobian Backup set for incremental backing up of set folders. After 18months use a problem has arisen. I am only able to delete about 150mb of files leaving 850mb as used space. I have not been able to open or view what is in this 850mb and have tried hidden files and a range of other options in Windows Explorer. Also when deleting folders the flash drive shuts down and has to be reloaded.