I have had the same problem with my N800 for the past few months. Started out as an intermittent problem and now the screen is barely usable. In fact, today was the first time I turned it on in a month, and since buying it a year and a half ago, I'd never gone without it for a day.

Seems to me there must be a loose or cracked connection, but haven't a clue as to how to fix it.