Does anyone know how to do a factory reset on an Olympus E-410?

I have recently been using the camera in varying degrees of weather, the joys of being british, and towards the back end of the week the camera was showing 'Card Cover Open' even when shut. This error seems to have resolved itself but in doing so the camera now seems to believe it is plugged into USB port even when not. Since this error i have tried and been successful in downloading pictures to computer, After this I then used the eject & safely remove hardware options, but even this hasn't cleared the error.