Why is “Turn BitLocker on” not available when I right-click a drive?
Some drives cannot be encrypted with BitLocker. Reasons a drive cannot be encrypted include insufficient disk size, an incompatible file system, or a drive is designated as the system partition. By default, the system drive (or system partition) of a computer running Windows 7 is hidden from display in the Computer window. However, if it is not created as a hidden drive when the operating system was installed due to a custom installation process, that drive might be displayed but cannot be encrypted.