13.10 won't start after upgrading

Solution 1:

You can boot your Ubuntu in recovery mode by following instructions on Recovery Mode - Ubuntu Wiki. It is recommended that you read through this page entirely before proceeding.

Just to give you a gist of the steps to follow in your case,

1. Enable networking in the same menu.
2. Select Drop to root shell prompt

3. Run command

   $ mount -o remount,rw /

   This will mount your partitions in Read / Write mode to boot from.

4. Just in case, if you have /home, /boot, /tmp, or any other mount point on a separate partition, you can mount them with the command

   $ mount --all

5. Run following command to repair broken packages that were damaged due to untimely reboot.

   $ dpkg --configure -a

6. To remount partitions back in read-only mode, run $ mount -o remount,ro /

   (If system says "/ is busy", skip to step 8.

7. Run $ sync
8. Run $ reboot to restart your PC.

Do let me know how it goes.

Source : Patrick's and Scott's answers.

Once you have successfully got access to your old Ubuntu, for upgrading to 13.10, I will recommend that you download Ubuntu 13.10 ISO and create a LiveUSB to boot from.

This will ensure that Ubuntu 13.10 download and upgrade does not eat your bandwidth while browsing. You will also have an additional option of Try Ubuntu and other cool tools that come along with a LiveUSB setup.