get an RA number and send it back, its a common problem.
but before you do check a couple things;
all solder connections
your battery plugs
do you have steering while its "shutdown" and until it re-arms?
is the esc loose inside its case.
another thing is that it would be helpful if you could post your complete setup on here (including the rx8s settings)
i had one like that too. after sending it back and having issues again, i decided i didn't want to run tekins anymore. it seems like they still have a few minor issues to work out.
the newest rx8s (3 hole case) has had no reported problems other than one i got which was due to an assembly flaw when the heatsink was bonded to the control board.
they are working hard to finally get all of the issues taken care of.