As jrog suggested your drive might be failing, or close to faling.
I did a quick Google after the response from fsck, and found this:
Lets try it!
And lets see the output, if it looks anything like the output from the link i posted (I haven't tried it, haven't had the problem before, so lets take it step by step).
sudo fsck.ext4 -v /dev/sda1
(Another thing you could try is, if you have tried it before and have the 'gear', is to remove the harddrive and put it in a USB tray and connect to another computer)