It's the LCD backlight not working. I repair laptops and it's the same principle. Bad news is it usually requires the whole LCD screen to be replaced as the backlights themselves are hard to repair/replace. Send it in for warranty repair if it's still under warranty.
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My N800: OS2008, Fanoush's initfs, SanDisk 4Gig x 2 SDHC, BoxWave FlexSkin and Sync Charger, Homebrew External Power Pack (4xAA NiMH Rechargeable 2400 mA)
Greetings from Sunny San Diego, California!