Ubuntu boots into terminal

Solution 1:

The hard drive is read only because it's got some errors on it. These have been detected during a scan and now your drive is read only. You need to run fsck against your main root partition while the partition isn't mounted or read only. It's read only so you should just have to run fsck.

If it's possible to run the LiveCD, you can use the gui tools to fix the issue, you can do all this using the System > Administration > Disk Utility once you're booted into the LiveCD desktop:

Once you've run the checks, make sure your disk isn't full (delete some stuff if you have to) and then reboot.