There are some issues today for me that my desktop can't boot as I expected, I installed windows 8.1 and ubuntu 14.04, yet only ubuntu 14.04 was booted, while the windows cannot. As a consequence, I try to do some recoveries.

First thing is first, I find the solution to booting problems, by using boot-repair.

As some blog wrote, I try following shell commands:

sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update”

sudo apt-get install -y boot-repair && (sudo boot-repair &)”

However, the command doesn't work for me, cause there are some problem poped out:

1. failed to fetch....

2. unable to locate package.

I tried some solution in the networks, such as clear the /var/apt/lists/partial, delete the lists file. yet none of them worked.

I look up to the ubuntu community, and found there is another command needed to be wrote,

sudo sed 's/trusty/saucy/g' -i /etc/apt/sources.list.d/yannubuntu-boot-repair-trusty.list

In my eyes, this command tells the system to add the yannubuntu-boot-repair source to be a trusty source, and will be used and downloaded as other trusty softwares. 
So it worked in the end. 

Now I can load both my ubuntu14.04  and windows 8.1 by using the boot-repair~

what a lovely day.