New build won't power up properly

Hello there,

I'm no expert at pc building and built my second pc today, with following specs:

CPU:Intel core ultra 7 265k

Motherboard: Mag B860 Tomahawk WiFi

Cooling: Mag core liquid a15 240

Ram: 4x 16gb DDR5 PC5-48000 6000mt/s

Grafics: GeForce GTX 5070

Power: Mag A1000GS PCIE5 1000W

Plus 2x 2tb PCIe SSDs

So, my pc won't generate any outgoing video signal, my monitor stays dark / says no video input.

• cable is slotted in gpu!
• monitor and cable tested and functional
• all 4 Ram are reseated, I tested every ram in every spot, single ram, all ram, just 2 ram, 3 ram.... I circled every stick, no change.
• gpu out and onboard-gpu tested, no change.
• Old rtx 3060 in (my old card, still in use and functional), no change
• Old PSU tested, no change
• Cmos resettled with button, no change
• Cmos battery out for ~10 minutes, no change
• Checked CPU, no damaged pins, cooler sits good
• flashed bios with newest bios; no change

When starting, ez debug leds of CPU are blinking for a second, dram is blinking a little longer, VGA is never on, and BOOT also never switches on, despite no OS installed.

All fans are spinning, but just no video output, slowly I'm raging here!

I tested with all extra ssds via sata in, without everything except cooling, and I don't know further. Besides, at first boot up, and every boot up after CMOS-reset the pc is boot-looping a few times, maybe 4-5, before exiting this loop and staying "on".

Which is fried, motherboard or CPU? Any other tips?

Kind regard