Why does my ps3 do this

You need to restore the file system.
Here is how to do it.

HOW TO GO TO THE RECOVERY MENU OF PS3 SYSTEM

1. Make sure the ps3 is plugged in (stand by mode).
2. Put out your usb cable for the controller and the controller itself (do not connect yet).
3. Hold down power firmly, ps3 will turn on and then turn off, release power button when t turns off.
4. Hold down power again, you will hear a beep and then a double beep, when you hear that double beep release the power button.
5. Now you should be seeing something in your monitor that say "Connect usb controller", do just that.
6. After connecting the controller press PS button.
7. You are now in the recovery menu.
8. To fix the problem of corrupt data you can choose #3.
9. If you want to format your hard drive choose #5. Be aware that this option will delete everything that is in your hard drive.
10. Remember that doing #3 and #5 is not 100% to fix the problem of corrupt data, I say about 70%.

Good luck!