Hallo Volker!
If there are no specific hardware errors signaled (you do have a sound at your pc for POST check , right ?) by POST sounds, I would make a visual control (motherboard OUT of the system, in front of you) of the motherboard and change the source. Statistically, in order, motherboard, RAM modules, power source is the culprit in main cases. It won't hurt to check or replace the windows kit you are installing it of. I would go further and check , too the power outlet, too. If you don't have a power outlet earth surge fuse (but I'm sure you do, do you?) accumulated electrostatic charges can make nasty surprises to your pc. Let me know your progress and I will assist further.
Unfortunately, when it comes to PCs, one has to "disect" every damn piece of it and trust "no one" if you know what I mean ;). "That is the way!" LOL
PS - In very rarely cases BIOS can die as a electronic piece of equipment. With a dead BIOS nothing works there.