First discover all the disks that your system has with:
sudo fdisk -l sudo blkid
It is best to use the blkid of the device this creates a more robust setup and allows for the disk to move around depending of scsi and apti booting.
One of these will be your system disk... DO NOT mess with this disk it its a sure fire way to brick the machine. The basic install partitions look like this:
Device Boot Start End Blocks Id System /dev/sdb1 * 2048 76068863 38033408 83 Linux /dev/sdb2 76070910 78163967 1046529 5 Extended /dev/sdb5 76070912 78163967 1046528 82 Linux swap / Solaris
Next rather that mess around with fstab and guess the whole thing fro scratch im going to use a GUI tool to mount the disks most of the way and clean up manually.
So to be safe we are backing up fstab first. if you brick it then boot from your install disk and copy the backup back over the top
sudo cp /etc/fstab /etc/fstab.20120412
Open the "Dash Home" (upper left) and search for "Storage Device Manager"..
Note that If you get nothing click the "More Apps" and then try the search again (the good the bad and then unity...) click it youll end up in the software center install it(the button is one the mid right). Then repeat the above step.
Now Storage Device Manager isn't bug free, the newer hard disks tend to confuse it. click each disk and confirm that the /dev/.. in the lower left corner matches to the tree layout if it does and it prompts you that your device is not mounted then go ahead and auto mount it.. it the text and display mismatch dont mess with it you can brick the machine. Also confirm that your not messing the the main system disk.
For example on my machine it confused sda1 with /dev/sbb5 ..
So once you run the tool or manually add the basic disk step you will want to mount each disk and confirm the they work. Then reboot and confirm that boot still works. Once your machine boots by that we can think about fixing permissions etc.
This page has an excellent listing of the basic options types to use to make the disk work well. https://help.ubuntu.com/community/AutomaticallyMountPartitions#Systemwide_Mounts