Start problems with the 944 Turbo

Hello, today, after a long time my old starting problem has occurred again. Short description: I get in, turn on the ignition, press the starter and the box, but does not work. I switch off the ignition and again on ……… (I do this sometimes once or twice, make it 10 times or 12 times) …… then it starts as usual. I have already renewed all relays, the DME relay twice already. Does someone have an idea what I could do? In order to limit the error? Temperature or weather-dependent the problem is not, it comes like that, or something like that, does not occur for a longer time at all, is then again once a week….. So really to get crazy. I am grateful for every tip! Greeting, Martin!