Quick reply...
Most likely, some flex connector went loose. Then you would better send N900 for repair, especially if you have warranty. Have you dropped the device recently?

Protective film could cause some problems, but not so abruptly.
http://talk.maemo.org/showthread.php?t=44517

If it was hardware issue with the screen, then at first only part of screen would be affected.
If the connector became detached (or short circuited or something else), then some other functions might be not working. Does the main camera work? The keyboard? The keyboard's backlight? The notification LED? The front camera? The proximity sensor? The microphone?