After install Ubuntu 16 LTS along with windows 8.1 64 bit OS.Its not bootable. I have install different partition but its shows ubuntu install successfully.When i start the computer only windows 8.1 fetch by bootable manager.Secure boot disable and UEFI mode selected.
Seems to me that the
Fast Boot option in Windows 8.1 is probably still enabled (which would just make your computer boot into Windows 8.1).
Do you get to the GRUB menu where you can select which OS to start, or are you using something else as a boot manager?
If disabling the
Fast Boot option doesn't help, could you boot up Ubuntu from a USB stick and check with
gparted if you have the correct partitions?