Thats what i was laughing at cos you forgot to re-insert the battery by reading your post lol anyhow go to this page it will show you exactly what to do and good luck take your time lol.

http://maemofanatics.com/how-to-flash-your-nokia-n900/

PS you CANNOT use Maemo Flasher 3.5 in W7 64 bit so your going to have to get to a 32 bit pc ok.