X570 Taichi - Error 00 flashing

Hello guys!

I just changed my I/O-Panel on my chassis (no other changes made) and also did some cable re-routing and management.

After reseating everything into the chassis, my mobo started to show error code '00', nothing else. I press the start button, everything lights up, fans start running and after about 20-30 seconds the PC shuts down and boots up again.

No signals are given out from the GPU, no USB externals lighting up.

The error code 'flashes' in 2-3 second periods (the numbers get brighter).

I also tried the following to fix the problem:

- tested two CPUs (Ryzen 5 2600X, Ryzen 7 3700X)
- flashed BIOS again via BIOS-flashback (3.0)
- reseated the RAM, CPU cooler, GPU, SSDs
- checked all of the cables, checked for shorting
- removed anything that isn't essential for starting up (only CPU, 1 stick of RAM and the essential cables)
- CMOS-reset, after that didn't work: removed battery over night
- tested all of the above points inside AND outside the chassis

I can't explain what happend here. I always do all the PC-building by myself, I do it whenever friends or family need a new computer, so I guess I got a bit of experience here. I always make sure the parts are disconnected from power and I try to 'drain' them by pressing the power button several times, I also make sure I am grounded (via bracelets usually).

I know for sure, that RAM and GPU work just fine, I couldn't test the CPU but it's unlikely there is a problem - it wasn't even removed from the socket during initial 'modding'.

Specs:
R7 3700X
G.Skill TridentZ F4-3200C14D-32GTZ (worked just fine the last 6 months)
2x Crucial M.2 SSD
Gigabyte GTX1080 'Windforce'
X570 Taichi

Has anyone ever experienced a similar problem? I'd be very happy if someone could help me out here.

As already stated, I installed another CPU that is working (on another mobo), but not on the Taichi. No reason for me to believe my CPU is dead.