I had a similar issue with my brand spanking new nokia n900. i just bought it from hong kong. I couldnt figure out for the life of me what was the problem. Even had it replaced by the same vendor for this issue. After swapping out the lcd and then the digitizer it finally dawned on me there was only one culprit left. The sliding mechanism which has a ribbon cable ot connect ot the logic board had to be the issue. after replacing it all worked just fine (the entire slide mechanism) symptoms included screen calibration intermittently being off, Not being able to touch the status menue intermittently, screen intermittently being simply 100 % unresponsive, screen imputs registering a cm below or above where I actually touched on the screen. hope this helps someone. pls msg if you have any questions.