Have done a disk utility this morning and it comes back with 'this disk needs to be repaired. Use the recovery HD'.
Reboot holding down Command R when you hear the startup tone. (or you can hold the Option key and choose the Recovery HD to boot from).
Then go into utilities and use disk utility to repair your MacIntosh HD. You have to boot from the recovery partition because you can't repair the volume you're booted from.
Retrieving data ...