I have read the 15 pages of this thread trying to find a solution for my power-on problem. Mine seems a little different. For two times my N800 (with OS2008, last revision) did not start when I tried to power it on in the morning (first power-on of the day). No power-on problems for the rest of the day. In both cases I opened the back cover to check that the battery was in place, I did not find anything wrong, then I re-inserted the cover, I pressed the power button again, and voila, the N800 powers on correctly. It sounds like the action of disconnecting and reconnecting the back cover, somehow, fixes the problem. Any idea about what causes this? Is it a hardware problem? I can still ask a replacement.