The Sony PSP uses the Sony memory stick as its way to save your game data. You can also use it to store your music and movies that you want to play on the PSP. Sometimes the PSP memory stick may become corrupted, and therefore unreadable by the PSP or any other device. Sony planned for this problem when it added a formatting tool inside the PSP software.
Turn on your Sony PSP and insert your memory stick into the PSP card reader.
Go into the "System Settings" menu on the PSP. All of the settings menus are located on the left side of the PSP menu.
Select the "Format Memory Stick" option from the "System Settings" page and click "X" to format the memory stick. Your memory stick will now be usable again.
Formatting the memory stick will erase all of your information on the memory stick.