Nope, as said above, with the device switched on, the power button does nothing, which does seem to suggest that the button itself is no longer working.

What is odd is that when I reflashed in R&D mode without the -R variable at the end, plugging into the charger or inserting the battery made the device instantly turn on (as expected) but it exhibited the same behaviour, ie booting circles appeared briefly then device shut down, but then reflashing with the -R at the end made it boot fully...