I installed Ubuntu 14.04 on top of my previous 13.10 Ubuntu installation. I did it manually by formating the mount and home folders without touching the Windows partition. Apparently it didn't detect the Windows OS.
But there is a 'Windows boot manager (on /dev/sda2) entry on the grub menu but it doesn't do anything. I can only boot into Ubuntu.
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.
Boot into Ubuntu. Terminal.
sudo update-grub
Then reboot. This should auto detect all boots and rebuild Grub.
