How to manually check Ubuntu version? (e.g. from hard drive)

You can use /etc/lsb-release for that:

~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=13.04
DISTRIB_CODENAME=raring

You can try chrooting into that system from another Linux or LiveCD. Let's assume your dead distro is on sda2. First, mount the partition:

$ mount /dev/sda2 /mnt

Now bind folders with crucial binaries to replace possibly dead ones. mount -B mounts one directory over the other one virtually replacing its contents, but without physically touching it:

$ mount -B /bin /mnt/bin
$ mount -B /sbin /mnt/sbin
$ mount -B /usr/bin /mnt/usr/bin

Now chroot to the old distro. chroot will pretend that given directory is / (so in our case we'll have a shell running in an offline distro, working on its files except for binaries we've bound before)

$ chroot /mnt

Now any command you issue will work as if that partition is your filesystem root. lsb_release -a will be executed from your binaries, but will read from files of the dead distro.

You can use chroot for many other things. For example you can upgrade Ubuntu without booting it: just boot a LiveCD, mount Ubuntu's partition, bind crucial directories like /proc etc. (do NOT binaries - this would update LiveCD binaries) and run do-release-upgrade in the chrooted shell.