The default fstab ion 12.04 looks like
but with your own/dev/sdx# names and UUIDs for the various partitions, and probably no final line for a floppy disk (shown in red).
# /etc/fstab: static file system information.
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc nodev,noexec,nosuid 0 0
# / was on /dev/sda1 during installation
UUID=01b9131d-43fe-4b4e-be2b-b319de5a898a / ext4 errors=remount-ro 0 1
# swap was on /dev/sda5 during installation
UUID=1bfd912d-b6b6-4a68-9aaf-4139513772ec none swap sw 0 0
/dev/fd0 /media/floppy0 auto rw,user,noauto,exec,utf8 0 0
If you have a separate /home partition you may need extra lines in the format
again with your own UUID for/home.
# /home was on /dev/sda2 during installation
UUID=e2554df2-7e16-4864-97c9-834d8bebecda /home ext4 defaults 0 2
You can find your own UUIDs from a live system by running
and it may be worth trying your own UUID version of this fstab, if you can't edit out the gibberish that you added with a live CD, as suggested by cortman.
sudo blkid -c /dev/null
I don't think running fsck from a live system will help as there is no filesystem corruption to worry about, just an incorrect fstab which is not allowing the system to boot.