Question Columbo-like repetitive no display/beep issue/circles spinning (mobo+cpu change inclusive)

Mar 30, 2020
Hello everybody,

as you might have already guessed reading the title above, I am exhausted- exhausted of looking for the cause of this really, really strange behavior my computer decided to bring on stage a couple of days ago- even Columbo would have his difficulties to solve this rare case, I am sure.
The last weekend my computer stopped working after more than 5 years devoid of problems. Suddenly was welcomed with the famous "No signal detected" message on my monitor, so I tried a VGA instead of the DVI-cable, same issue. Then I plugged the monitor on a laptop, and the screen was appearing, so the monitor is fine.
Next I thought about a malfunction of the graphics card, but its twin fans are spinning, and I thought about giving trying to boot with a minimal setup:
- Only cpu, motherboard,psu connected, power up => No beep!
This started to puzzle me, no beep?
So it's the motherboard or CPU?
I bought another mainboard 970A-G43 with a FX6300 CPU bundle, the same components I had installed in my computer. And the first I did was to check for the beep:
What a relief! It was really there, I could hear it. Then I added the rest of the components and got my computer working again. From dusk till dawn...
The next morning I got another "No signal detected". Oh no, can you believe how I must have felt that morning? Devastating, isn't it?
So I thought about possible reasons: Short circuit? But I had installed the motherboard with the spacers in between motherboard and case.
The PSU? Its (beQuiet Dark Power Pro P10 650W) fans are turning, and the CPU's and graphics card's fans, too, so what is going on?
I am stuck at the moment. No further ideas. Might the PSU cause this strange scenario? Do you have any further ideas what I might test? Is the motherboard and/or CPU broken (again)?
Or is the PSU just playing a game with me?

Thanks in advance.

EDIT: There's one hint I might have forgotten:
The morning after installing the new components, I got a message, that I need to set my BIOS settings again. After setting time, et cetera, Windows showed the wrong time, so that I had to update time
manually. Only some hours later the "No signal detected" message appeared at screen again. I do
remember that I did have this BIOS message in the past, too, a couple of times. Might this be a hint
toward the cause of the real problem? The PSU?

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