I hope your assessment of the hard drive failing isn't true. My laptop is only a year old and I have used only around 40gb of the available 1TB hard disk space.
I was lucky enough to get an error dialog when I tried to open the terminal in one my sessions and used that error message to trouble shoot the problem and by the looks of it, it is fixed for now.
I got a "Failed to execute default terminal emulator. Input/Output error"
One of the ubuntu forums had a fix involving XFCE. I don't remember the exact fix but I just looked at my terminal command line history and these were the codes associated with XFCE (some of them I remember turned up an error like no such file or commend - sorry for the really non-tech explanation
xfce4-terminal -x htop
sudo ln -s /us/lib/x86_64-linux-gnu/xfce4
But I think this fixed it, although I have no idea what it did and how
I will monitor the situation for the next few days and hope that it doesn't show up again in the near future (Until June 2016 atleast because that is when I defend my thesis).