Thanks much jiggling the charger worked fineHardware problem.
Try plugging in a charger and wiggling it around while you try to scroll down. Also squeezing the case around the trackball can be helpful.
The sensor for trackball movement is part of the same board the charger plugs in to.
I've never heard of a way to navigate the recovery menu without using the trackball.
This is a common problem and one I'm personally very familiar with.