your battery seems to be empty in a way the phone doesn't start.. the n900 does boot into charging mode inorder for the battery to charge (blinking yello/orange led) , if the battery is quite empty , the charging is managed by the hardware battery chip , in that charging mode , you can't start the phone and the led will have a solid yellow color . connect your phone to your pc / charger and leave it connected for half an hour and let it charge .