felbuts, it could be as jensbw suggests - the battery could be dead. That's a catch-22 situation, because the device always runs through the battery (even when connected to a charger), and when charging, even when "off", it's actually booted to a semi-up stage where it can run some software to manage the charging.

However, as far as I know the battery in the N900 is also used in other phones so it should be possible for you to either loan a battery which is charged, or, maybe simpler, get your battery charged in someone's phone (maybe they would be helpful down at that Nokia center).