I once used an incorrect firmware (for the CPC core) in conjunction to something else which "blocked" my MiST during the firmware update. I don't remember how the blinking was, anyway for your case it might worth trying this (it's what I did for my locked MiST and it worked):https://github.com/mist-devel/mist-boar ... heFirmware
Use Sam-Ba but you probably know this since you talked about the JP1. Shortening JP1 is really easy, just use a paper clip or something similar.
MiST board are supposed to be checked before sending them to customers, so we can assume your was working once. Could it be during shipping, like some shocks or magnetical fields?