Unlikely that it's power since all the other boards were powered the same way, so it's good to know that it's probably not a hardware issue.
We do have a reset button. I can use it successfully with the short press to update the firmware, but the 5-second press doesn't work unless I'm able to connect the IDE and run reset(true) first. Of course I can't do that since it won't connect to the IDE.
Can you clarify what mean by "If that works then you really should be able to just hold it and boot without loading any of the saved code - and it should appear as MDBT42... again." - Is this different from holding it while I power it on for a hard reset?
I have tried uploading new firmware but that didn't change anything. Probably because we had 'save on send' set to flash - execute code at boot. even after reset.