All I have is the reset button which is probably what you are talking about. I tried resetting dozens of times, and it simply wouldnt work -.-
But whats important now is the screen does seem to be damaged. Do you know any way to help reverse the effects?
As like any screen, they are not designed to have more power forced into them, the reset button is not what I am talking about, this just resets the pda, but doesn't cause any memory loss as such, which is what you want.
As pictured below on the example PDA there should be a button similar as such, turn that to the "off" position. If this doesn't help your PDA is probably damaged.
http://homegrownforums.com/images/pda.jpg
However if that doesn't work, you can try holding a magnet up to the screen, maybe it can rearrange the LCD crystals? But be carefull to do it only for a very short period, and use this as a last resort.
Good luck man.