same problem i had mate. 1 second left on NSU and then thats it. it seems like this is gonna be a problem for a lot of N900 users. NSU bricks some of the phones. im gonna test tonight another battery and see if it works to. i think nokia need to make some sort of recovery proccess as this isnt working out. try this. put your 5800 fully charged battery in your n900. then 1. remove battery 2. connect USB cable 3. start flasher-3.5 from command line 4. insert battery 5. flashing starts