Search for a posting by user "estel" on the reboot issue. It is a known but very elusive bug.

To summarise: shutdown always works but trying to do a reboot does not, as the device tries but shutsdown.

Another peculiarity: if charging when off it may not boot up when switched on. Uncouple charger and switch on, and it will boot.
No known cure. My n900 has done this in the past. No after a reflash is doesn't.

"Technology is strange"

(edit: slow typer I am , and long winded....)