I've just received my brand new, never used N800 and it did exactly the same thing. I was able to get it to work for about 10 minutes with the new battery straight from the box, but then I decided to charge the battery while I did some work. That's the last time I ever managed to turn it on. Plugging the charger in would bring up the 'Nokia' logo, followed by a small (static) battery icon, which then dimmed considerably and then the screen went black. No amount of pressing the power button would do anything. A couple of times, the blue led on the navigation button lit very briefly, but then straight back to a black screen. The charger felt cool to the touch. I removed and replaced the battery a number of times (which also felt cool). In the end, I just packed it up and returned it as DOA. I hope the replacement works! It is a worry seeing a number of entries about this problem.......