if flashing RAPIDLY then your transponder in key is not being read. try using spare key [key has a transponder /chip built in to it,] if you look on edge of plastic part of key you will see a red or blue plastic insert make sure it has not fallen out in which case you may have lost transponder. if so your system will need re-coding [try a locksmith to see if they have kit to do it.]unless you have a master key [red].
k
January 2010