Instructions
Use the thumbstick or the directional pad to scroll to the "Settings" menu. Scroll down to "System Settings" and press "X."
Scroll down to "Format Memory Stick," and press "X." A prompt will ask if you want to format the Memory Stick. Select "Yes," and press "X." Another message warns that all your data will be deleted. Select "Yes" again, and press "X."
Allow the formatting process to complete. Scroll to the "PlayStation Network" menu on the main menu. Scroll down to the "PlayStation Store" icon, and press "X."
Browse the store for all games you previously downloaded. Add them to your cart, and download them as you did previously.
Select "Game" from the main menu, and scroll down to the Memory Stick icon. Press "X" to open it, and you should see all your games listed.