yes, as Maxximuscool pointed out, I'm pretty sure I remember people saying that you can use an external charger to revive it in this situation.

before doing that try this: take out the battery, and press and hold the power button on the N900 for about 2 minutes. then put it back in without SIM or memory card and try again.

otherwise ext. charger is the way to go. or find someone who has a Nokia 5800 and use their battery (to test your phone make sure its still alive and to charge your own battery)