Two days after re-flashing to PR1.2 and re-flashing the emmc, when I powered on the N900, it never reached displaying the NOKIA screen in the boot process. I retried powering on the device several times, and the failure was the same.
About a week later I go around to attempting to re-flash it again, however now I cannot even get the device to power on, and so cannot flash it. When it is plugged into a charger it does not appear to charge normally, the indicator light displays an unblinking orange light.
Any idea what the problem might be?

Have you removed the battery for a while and replaced it again?

Yes, I had it out for a full 24 Hrs. Placing it back in did not change the situation at all.

Bumping this up.

Unblinking yellow light means that the charger chip is operating autonomously without software control.

Usually this would mean that the battery is too empty to be able to power up the device.

Are you using USB cable or the wall charger to charge? Please use the wall charger in this situation, and leave it on for a few hours.