This is what you need to do.

Take a screwdriver and unscrew the blue screw and then pull out the hard drive. (Don't unscrew the other screws, just the Blue one).

To pull out the hard drive you need to take the little metal handle and pull it to the right, then pull it out towards you.

After you take out the hard drive, just put it back into the PS3.

To put the hard drive back into the PS3, use the little metal handle on the front of the hard drive and push it to the left while the hard drive is inside the PS3.

This has happend to my PS3 when I first got it and after I took out the hard drive and put it back in, it solved the problem.

I called Sony Customer service and they told me to do this as well, so it should do the trick.