Instructions
Power on your PSP and navigate to the "Settings" tab in the Xross Media Bar and select "System Settings."
Select "Format Memory Stick." This will erase all of the data on your memory stick and reformat it for the PSP. Any files stored on the memory stick, including any viruses, will be deleted.
Select "Restore Default Settings" from the "System Settings" option. You will be prompted to confirm that you want to restore the default settings. Confirm by selecting "Yes."
Select "Yes" again to confirm that you wish to continue. All of the systems settings will be restored to their factory defaults. Any viruses stored on the system will be removed.