Cannot boot to Windows 8.1 after installing Ubuntu 12.04.3

Question

I installed Ubuntu version 12.04.3 on my desktop and after that I cannot boot Windows. The computer has two hard disks (one is 2TB, one is 1TB). Before I installed Ubuntu, I have Windows 8.1 installed on the 2TB hard disk. The 1TB hard disk is empty (no partition, no logical drive). I installed Ubuntu in the following steps:

(1) create a Ubuntu 12.04.3 installation DVD

(2) boot from this DVD

(3) Ubuntu installation program shows the following disk partition:

/dev/sda (2 TB disk with Windows 8.1 installed)
/dev/sdc (1 TB disk, empty, no partition)
/dev/sdb (32 G flash drive)

(4) I created two new partitions on /dev/sdc (1 TB disk):

/dev/sdc1 (ext4 format with 968 GB)
/dev/sdc2 (swap, 32G)

(5) I chose to install boot loader on /dev/sdc (1 TB disk)

(6) Everything was very smooth. But after I restarted the computer, there was no Windows boot option. It directly boots to Ubuntu 12.04.3 user loggin screen. Ubuntu still can access Windows 8.1 disk (/dev/sda, 2TB) and I can access all the files there. But I cannot boot Windows 8.1.

(7) If I unplugged the hard disk with Ubuntu installed (i.e. /dev/sdc with 1TB space), the system still cannot boot Windows 8.1. It stops with the "grub" prompt.

Can anyone help with this problem? Thanks.

Answer 1

Boot-up to ubuntu, fire-up synaptic or ubuntu software center, install grub-customizer go to general settings, in visibility check "show menu". And don't forget about askubuntu site ;)

Answer 2

if you like to do a test without changing a single bit of the current content of the hard disks on that PC, you can start by creating a bootable CD / USB stick with SuperGrub2

https://www.supergrubdisk.org/super-grub2-disk/

this tool can automatically scan and identify the OSes on your hard disks, so after booting from it you can verify that you can still boot also in windows. After that, for a more stable solution, you can proceed with grub-customizer as described in the previous answer