What you will need:
Experience with these things.
This happens when you maybe mess up with the online spoofer, etc.
1. You want to download the official firmware of whatever your jailbroken PS3 is using (3.41 - 3.55).
2. Get your USB device, on your USB make a folder called "PS3" with caps!
2. Within in that folder make another one called "UPDATE" with caps!
3. Put the official firmware in the "UPDATE" folder.
4. Put the USB in your PS3, go over to settings.
5. Select the update system, choose via USB Device
6. Follow the on screen instructions!