I am unable to boot into Ubuntu 12.10. I have Windows 7 installed as well. The GRUB seems fine. I can boot into Windows. But when I boot into Ubuntu , the following appears.
"no matching password file entry in /etc/shadow add user 'varun'"
This means your /etc/shadow file is missing user varun. Information about the /etc/passwd and /etc/shadow can be found here.
Use a live CD or a GRUB rescue prompt. For the 2nd one follow the answer with images here How do I reset a lost administrative password?
Have a look at your /etc/passwd file with more /etc/passwd|grep varun and at your /etc/shadow file with sudo more /etc/shadow|grep varun. if the 1st does contain a line and the 2nd does not you can re-create your shadow file with the command
After that you can use passwd varun to create a new password.