I faced that problem when I installed Ubuntu 14.04 LTS alongside my pre-installed Windows 8.
After installing Ubuntu I ran the recommended repairs in Boot Repair. However, the grub menu disappeared and my laptop booted straight to windows 8. Inside windows I opened a command prompt as administrator and typed in this command exactly as it is:
bcdedit /set "{bootmgr}" path \EFI\ubuntu\grubx64.efi
After it concludes successfully just restart your computer and grub should turn up with functional boot for both Windows and Ubuntu.
I strongly recommend reading this though. (if you have not already)
A small tip when installing Ubuntu using the “Something else” option, create a swap partition (if you have not done that already) that is twice your RAM size at least. If you have an SSD then just forget the swap partition.