Another "me too" story very similar to the one quoted above. My place of work ordered FOUR N800's. Three were good, the fourth has this "can't start" problem.

It worked the first time out of the box. After playing around with it for awhile, I shut it off. It would not restart. Completely black screen, and no blue light around the control buttons when the ON button is pressed.

Went to the web and found this thread. The only thing that worked for me was to keep the charger plugged in until the "charging" icon magically showed up on the until-then blank screen. (It took at least 1/2 hour for the charging icon to appear after plugging in the AC adapter.) I could then start the unit.

After finally getting the N800 to start I shut it off (pressed the on/off button and selected "Shut down" or "Turn off" or similar from the menu) and left the unit in the charger overnight to make sure the battery was fully charged.

In the morning, I unplugged the charger and tried to start the unit. No good. Completely black screen, no 'blue light' when the ON button is pressed.

Drove to work. Unit started fine. A miracle cure! Shut it down. It would not re-start.

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Since I had a perfectly good unit to work with, I determined that IT IS NOT THE BATTERY OR THE CHARGER. I took a fully charged battery from a 'good' N800 and inserted it into the 'bad' unit. The 'bad' unit still was 'bad'. Same for the charger.
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I suspect it's a problem with the unit's "sleep mode" as others have pointed out. To the best of my recollection, this is what I did with the 'bad' N800 when I took it out of the box:

- Inserted supplied 128 MB memory as per instructions.
- Inserted battery.
- Plugged in AC adapter (saw 'charging' icon but DID NOT wait for battery to fully charge)
- Started unit and played with it. Everything fine.
- Shut down unit - AC adapter is still plugged in.
- When I saw the "Battery Full" indicator, I unplugged the AC adapter.
- Troubles began, as per above description.

So... not wanting to trash another N800, I was careful to let the battery fully charge before starting the 'good' unit for the first time. Have no idea whether that contributed to the problem.

Another observation, which others have pointed out. When you shut down the N800 with the AC adapter plugged in, it goes into some sort of 'sleep mode'. Leave the AC adapter plugged in, and restart you'll get a quick start without a 'progress bar'.

If you shut down the N800 with the AC adapter unplugged, it truly shuts down. It takes longer to start, and you'll see a "progress bar".

So what happens if you shut down the N800 with the AC adapter plugged in, and then remove the AC adapter? Is it still 'sleeping' or does it turn off completely? or does it turn itself into a useless piece of crap?

Call me suspicious, but I plan to never run the unit with AC adapter plugged in to avoid this problem.

I don't want to trash another N800, but maybe someone would like to trash theirs for the sake of science! At your own risk, try these steps and tell us if it ruins your N800:

1) Run the unit on the battery for awhile so it could use a recharging.
2) Turn the unit off.
3) Insert the AC adapter and wait for the "charging" icon.

LEAVING THE ADAPTER PLUGGED IN:

4) Start the unit. Play with it for awhile, but not long enough for the battery to recharge.
5) Shut the unit off (AC adapter still plugged in)
6) Wait for "battery full" icon.

7) When battery is "full", unplug AC adapter.
8) Try to start.

Did the above trash your N800? Anybody?

I have to believe Nokia knows this is a problem. For every one of us that takes the time to report the issue on this forum there must be many more that have failed units who are silent about it. Nokia, are you listening?