Question No signal on monitor

[FreamoN]

Hello, few months ago I sold some parts of my PC and haven't used my PC since.
Today I decided to build new PC, but leave the old PSU and old Motherboard on the PC still.
I bought NEW parts :
3070 Ti,
Ryzen 5800x,
2x8 RAM Corsair 3600 Mhz CL 18,
H150i Elite AIO and some new fans for the case.

My OLD parts before I sold them :
Ryzen 3800x,
2080 TI,
2x8 GB RAM G.Skill 3200 Mhz
Kraken X73.

Both are on the Motherboard Asus Prime X-470 Pro and PSU Seasonic Prime Gold 650W
I press the start button and voila, RGB lights on, all fans work, GPU, PSU and AIO fans work too, but no beep and no signal on the monitor at all.
Whenever I take the monitor cable out and in of GPU it shows me that it works, but saying no signal and goes full black. The monitor works when I connect it to my TV.
What might be the issue here?
Yes, all cables are connected I went through them hundred times and all connected. I also don't have older CPU on hand to test it.

I also tested older CPU, AMD Ryzen 3200G, which has the same BIOS version as the 3800x, still nothing. No signal on the monitor. Tested also on fully new PSU from Corsair due to maybe more Wattage needed, still nothing.

The only part in my PC that isn't new is the Mainboard from Asus.

 

[FreamoN]

So I made it work somehow.

I took out the 3070 Ti GPU and put the 3200G CPU with integrated graphic. It worked, I was able to boot the PC. Went to BIOS and updated to newest BIOS version. Now the 5800x and 3070 Ti work and start the PC. However, whenever I put my second RAM stick (Another 8GB) the PC won't boot anymore. Is the second stick dead?