I keep trying to find help for you in the big wide interweb - lol.
Ther are many devices out there which have, or are suffering from what you currently describe.
One post claims that when you get the little green android and the exclamation triangle that you are in stock recovery mode but the tablet can't access it. I don't know if this is true or not.
However, many seem to have been resolved (if all the posts are to be believed) by doing this:
Power button + up volume= recovery = red triangle.
red triangle+power button+up volume= other menu
other menu+clear cache=other menu
other menu+reboot system= happy
Can't do any harm in trying it.
