First of all, saying he should buy a new one does not answer the question. It is passive aggressive nonsense and doesn't do anything to help.
Now!
Here's how to fix it.
Step one.
Follow the instructions provided by this kids video (skip to 40 seconds and the kid finally gets to the point) be careful and mindful of everything you do, and please unplug your playstation before you do it so you don't electrocute yourself.
Second.
Now that you've done the basic cleaning of your hardware, we're going to clean your soft, because I guarantee this happened just after you overloaded your system storage with a game/app/file that was just short of the storage line.
OK.
Once you've done what was said above,
Preform the system fix as the playstation tells you to.
(Don't worry, it will only take a few minutes and not the 2-3 hours playstation says it could.).
The system will reboot.
Once it does, find a large game file and delete it.
This should free up the much need room your hard drive needs to remain efficient, quite, and quit giving you the bullshit message you came here to fix.
For any other tips or questions, feel free to email me at vincenzomarsden@gmail.com.
Happy gaming!
Cheers!