If you ever see the UNMOUNTABLE_BOOT_VOLUME error this does not necessarily mean all is lost.

Most users would use the Recovery Console and execute the command CHKDSK /R Under normal circumstances this will fix most problems, but not all.

If you encounter this problem then try the following:

Try CHKDSK on its own with no switches. This will still find and fix disk errors.

Reboot

If this does not resolve the problem try booting into SAFE MODE.