Grub not working after Windows 8.1 update on Ubuntu 12.04 LTS [duplicate]
Solution 1:
I had this problem too. After updating to Win 8.1, installing boot-repair in ubuntu & running it didn't work for me. (But it was working earlier. Also note that I have to use boot-repair disk after every windows update - every month - since updating to windows 8.1. Before that this problem was not there)
Instead create a bootable usb with boot-repair.
Download iso here: boot-repair-disk
Boot into this & select recommended repair. It will solve the problem.