• Restart your Mac holding down "Command(the Apple key)+S" key to enter 'Single user mode'.
• Type "fsck -f", and hit return.
• Once complete type "reboot" and hit return to reboot you Mac back in to OS X as normal.
If there is anything that you think is wrong here, or you think I have missed any vital steps out, please post and let me know so that I can amend this.
Resetting PRAM and NVRAM
Shut down the computer.
Locate the following keys on the keyboard: Command, Option, P, and R.
You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.