I had more or less same problem a week days before.Prior to that I had to wait for almost one month with my N900 not booting. Don't panic as I did.Really I too have exhausted all the options. I read and re read the wiki in vain. What you must do is to follow the advices of reinob,joerg_rw to the letter.
1.Don't go for cold flashing
2.Re download the images
3.flash combined first,emmc later
4.check the usb cable.
5.In my case battery was at fault.Bought a new battery.problem solved.