Sometimes if I've left either my 954 or 929 for a long time I have to cycle the ignition a good few times then hit start. Think maybe the fuel pressure isn't enough with one prime of the fuel pump if the rail and injectors are dry or maybe the hiss doesn't pick the key up first time. I would double check all the basic connections like earths and and the killswitch etc encase they are corroded and drawing power. Have you tried again since?