airport extreme won't reset

I can not remember the password for my Airport Express (may2013), and am trying to do a factory reset. I disconnect all cables, reconnecting power while holding the reset button pressed. The light turns green, then after some 20 sec blinking slowly amber light.

It´s like the reset button does not work. I have only used it once before, and I know for shure it worked then. Anybody have a suggestion?