Hmmm. I honestly think something might be royally screwed up. When you run "killall bme" - as done to do that hot-swap-battery hack - the LED goes constant yellow until you restart it.

This to me indicates that it's likely yellow LED is a default set by Nokia for battery-related fail. You did hold the U key while plugging it in to flash? Anything happen on the computer end? Did it try to install a driver?

I suspect something may have broken at the hardware level - perhaps a chip or some bus that is needed for BME to properly communicate with the battery.

You MAY be able to use the flasher to put your N900 into R&D mode, and kill the watchdogs. That way you may be able to boot it, and see if you can at the very least test if BME and other lower level stuff is loading/communicating correctly.