The
level wheel has always been something of an issue with the 300 - IIRC it's pretty much just a rubber band which actually makes it work, linking the wheel to a sensor. If you're confident about it, open the
desk up and have a look to see if the rubber band has perished or fallen off - I'd be fairly confident in betting that that is the trouble. The
Page Up/
Page Down keys I'm not so sure about!