Recovering Grub after installing windows 8.1 [duplicate]
Solution 1:
You just need to install grub again with an Live CD. This link could help you
Solution 2:
use easy.bcd in windows.download easy bcd from Internet run it on your windows now from the side bar select add new entry then go to Linux in upper tabs select grub 2 write name Ubuntu and select add it's done. now whenever you boot from next time you will see two options name windows8 and ubuntu select that one in which you want to go