Well, it seems that I have much bigger problems now.
After a memory exchange the motherboard does not boot anymore. Only the Power LED on the onboard switch is working but pushing it results in nothing anymore.
Then I put the old memory back, and also then no booting anymore. Dead.
Another powersupply and the mobo came back to life, but only a few seconds, but now at least I got to see code 55, after that it goes rebooting again, and code 55, rebooting, etc. Also no videosignal.
What does that mean, 55, something in the CPU initialisation?