I don't know the exact answer.
For a start, I would like to enter the bios somehow.
!! If we can’t get into the bios then that’s a big problem!
Inspect the pins on the processor and the slots on the motherboard with the light to make sure everything is 100% good
Check to see if you have an inflated capacitor on the motherboard.
(most often these around the processor, but look at the others, it mostly looks bold)
Also do you have content drying from some component (dielectric)
Check to see if you have any screws left on the motherboard.
Basically there is nothing else to be a problem other than the motherboard.
Today, motherboards are severely damaged because the maximum performance for the most economical materials is squeezed out of them so that I can sell them for a cheap price. So everything bothers them, first of all that there is some short circuit during the installation of new parts.
I recommend that you always save the bios on usb, put a cap on the CMOS and use rubber gloves.
See if your motherboard touches the case somewhere. Just put it on the slots on the case and watch the other cables so that they don't get caught under it.
When you have checked everything visually, take the motherboard out of the case, connect it to the power supply, leave the processor and the cooler on it. (Return CMOS to the correct position)
Connect the tested monitor to it via the hdmi port from the motherboard, remove each M.2 port (Nvme) and everything that is not needed for the BIOS to work.
So only motherboard, power supply, processor, cooler, monitor, 1 Ram slot in DIMM2 (probably) (try first or second of sockets)
Turn on the computer and if there is no picture, check each part separately.
A screen on the motherboard that gives the Qcode of the motherboard would help a lot here.
The last thing I would do was take out absolutely everything from the motherboard leaving only the power supply (no processor and dimm)
put a new bios that you will download from another computer and put on another usb and run mbo upgrade bios.
You have explained how it is done everywhere on the net.
If that doesn't work either I would take another motherboard.
This has been translated from google translate so I apologize for the mistakes.