Most likely the hard drive has gone bad.

You could try reseating the system storage drive which is located inside a compartment on the side of the PS3. It will require a phillips head plus screwdriver to take out the hard drive secured to the hard drive cage as a screw stops it from being taken out or moved.

Here's a guide on how to replace the hard drive if it is faulty:

PlayStation 3 Hard Drive Replacement

You can buy the hard drive from here:

500 GB 5400 RPM 2.5" Hard Drive

Or literally any 2.5" hard drive or SSD will work as well. Just make sure it's at least 120GB or more. You will most likely need to download system software when installing a new hard drive.