Sony Reader 350 (PRS-350)

Factory Resetのやり方。MobiRead Wikiより

Sony PRS-350

(Tested on PRS-350 - this probably also works on the PRS-650 - courtesy of [7])

Power off the Reader Digital Book.
On the bottom edge of the Reader Digital Book, using a thin object such as a paper clip, press the RESET button.
Turn on the Reader Digital Book.
While the screen displays Opening book... , simultaneously press and hold down the Previous Page Turn button and the Size button until the Reset All screen is displayed.
In the Reset All screen, press the OPTIONS button to delete all content, restore all factory settings, and clear the DRM authorization state.