Thanks KarlosDaJackel,
there've been some issues with integrating the new motherboard (possibly, the existing power supply is not strong enough for the new CPU - having the CPU put in, the computer would start but instantly stop again - without the CPU, the computer would not output anything to the screen - nevertheless, the power supply would stay on and the harddisk make noise) (there'd been a problem with my screen, too - got a new monitor in the meantime).
So I switched back to the old hardware, temporarily.
Anyways, there's a new problem with that old hardware, and I posted that as a
new thread.
Thanks sincerely
robbbert