Have an external hard drive but notice that on Windows 7 the drive file system sometimes fails. The reason for this that Windows 7 likes only the NTFS format. All other old file formats like FAT32 tend to be ignored. The only solution to correct this problem is to format your drive to NTFS so that Windows 7 will always recognize it.
There are several ways to do this and one way to do it is by using the convert.exe command in DOS. After you type
convert.exe convert x: /fs:ntfs, (in which x is the drive for your external hard drive).
Make sure that your external drive is empty first before your convert it to NTFS otherwise all your data will be erased.
ex:
c:\users\ED>convert f: /fs:ntfs