I have cloned my system drive to another partition, but it doesn't show in the boot menu (the one that comes with Windows 8 where I can select OS to boot).
How do I fix this?
EasyBCD can easily detect the partition and add an entry in the boot menu. If it does not work, try to mark the partition as active in the Disk Management (search in start screen).
You can boot using the Boot-Repair Disc, which comes with Boot-Repair pre-installed. You can use gparted to mark the partition as active/bootable as well.
More instructions can be found here