Will run through them again, I am using machine in question now as fault is intermittent.
Intermittent is not good - could be a sign of a failing hard drive.... Hope you've backed up any and all important data in the event intermittent becomes permanent.
Is this a PC or laptop? If PC, get another Hard Drive - you can get a 1TB drive for under $100. If you buy retail (not OEM), many include software such as Acronis to allow for easy transfer of data / OS / etc....
A laptop would be a bit more involved...
Best Luck :)
PP