My new n800 also will not turn on after power off. Same problem out-of-the-box, and now with os2008 flashed. Will not charge either.

Turns out I just need to leave it for a few minutes. But I'm worried it may get worse. I'm in Australia, and bought from a US ebay seller, so warranty repair will not be easy. (But the purchase cost in Oz is double - why!?)

Someone suggested a software problem with shutdown, so i tried just dropping the battery out while on, but it still would not turn on again for some minutes.

If it doesn't get worse, I can live with it, but I ordered a couple of spare batteries, and swapping them will not be fun.