I'm running Ubuntu 12.04 and am fairly new to it. My machine has 3 hard disks, 1 (ext4) 2.0 TB for Ubuntu and home directories, 1 (ext4) 1.5 TB to be used presently when I relocate all /home/ directories for the whole /home/ tree, and a third drive for backup (ext4, 1.0TB). The machine picked right up on the first disk, did the Ubuntu install, etc. 1.5TB and 1.0TB disks are shown at upper end of directory tree when I use the built-in directory tree traverser (icon is a couple of folders, don't know program's name). Yet when I try to mount either disk 2 or disk 3 by right cliking them and picking "mount" they won't do it. If I use fstab to automount them with lines at the end of the file like:
UUID=long--string-here, gotten by blkid /media/ ...
the machine during boot says there's a problem mounting the drive, and asks if I want to skip it.

I also tried using "mount" to mount the disks, but with no more success.

I also have similar problem with external 1TB drive, but it's NTFS.

Any helpful guidance would be much appreciated.