USB Flash Drives not working?

FAULTY FLASH DRIVES
Sometimes when a flash memory stick or USB external hard drive fails because it was not removed from the USB port properly. If the device is removed by just pulling it out of the USB port, it can cause the flash device to fail, you must click on the Safely Remove Hardware icon on the Task Bar and select the device you wish to remove and only do so when instructed to do so.

When the flash memory USB hard drive device appears to malfunction it maybe possible to restore it by reformatting it. Insert the flash or USB hard drive into the USB port then Click on Control Panel - Administrative Tools - Computer Management - Disk Management.
Then right click on Disk 1 removable drive and click Format. After the flash drive has been formatted it will indicate that it is Healthy.

You need to format the flash or external drive. Format the drive as primary drive and in FAT32. (FAT32 will allow data to be exchanged between MACs and PCs also between XP/Vista and earlier versions of Windows).
Otherwise format the USB flash drive in NTFS.
Insert the flash or external hard drive into the USB port then Click on Control Panel - Administrative Tools - Computer Management - Disk Management.
Then right click on Disk 1 removable drive and click Format. After the flash drive has been formatted it will indicate that it is Health

Many people still don't realize this, but flash memory wears out the more you delete and write files to it. How quickly it wears out will depend on the specific flash drive. Like anything, there is a wide range of quality in currently available flash memory-based drives. You can make a rough correlation with the cost/quality of the device (what you pay is what you get), but even that tends to change over time. Depending on usage and quality it could be talking as short as months or as long as several years. In extreme cases of misuse it could lasting as little as a few weeks.