GNU GRUB Terminal - Instead of Ubuntu login screen

If you have installed without Wubi.exe:

At the grub prompt try these commands:

set pager=1
ls

Now, suppose the output of ls is: (hd0) (hd0,msdos2) (hd0,msdos1), in order to find the linux root filesystem run:

ls (hd0,1)/ which should give you all the files/folders in / such as bin/ boot/ cdrom/ dev/ etc/ home/ lib/ etc.

Once this is done continue with:

set root=(hd0,1)
linux /boot/vmlinuz-3.13.0-29-generic root=/dev/sda1
initrd /boot/initrd.img-3.13.0-29-generic
boot

Of course replace vmlinuz-3.13.0-29-generic and initrd.img-3.13.0-29-generic with what you find in your /boot

/dev/sda1 is the location of the root system. You may have to change it if /dev/sda1 did not work.

If you have installed using Wubi.exe:

If you have installed Ubuntu using Wubi, perform following steps as given in the WubiGuide:

1. boot into Windows, run chkdsk /r from Windows on the same drive where you installed Ubuntu, shutdown cleanly and then try to boot into Ubuntu again.

2. if still not good, check that you have a C:\ubuntu\disks\root.disk file. If this file is missing, boot on Windows, open the Windows Explorer, set it to be able to see hidden folders, then look for a hidden folder called C:\found.000 or dir0000.chk . Move the files from found.000 to their original location inside the \ubuntu\disks directory. You may have to rename it into root.disk.

Run those commands

grub> linux  (hd0,1)/vmlinuz root=/dev/sda1
grub> initrd  (hd0,1)/initrd.img
grub> boot

Replace hd0 with your hdd number and /dev/sda1 with your partition holding the /boot mainly the dafult will work if you don't have more than one hdd and with default installtion

check this for more info

When you can boot again you should fix your problem

sudo update-grub
sudo grub-install /dev/sda