Mac Pro Late 2013 "trash can" won't turn on

Hi,

My Mac Pro Late 2013 suddenly doesn't turn on anymore.

The white lights on the backplate turn on but when I hit the power button there's no sign of booting.

No fan turning, no sound signal, just silence...

Two days ago everything worked fine. No clue what happened.

I already tried a few things:

1. Checked power supply (cable, power socket)
2. Disconected everything except power, display, mice and keyboard.
3. Disconected everything except power.
4. SMC Reset (Plug out power cable, hold power button for 15sec, put power cable back in, wait 15sec, press power button)
5. Plug out power cable and wait 24h, hold power button for 15sec a few times during that period.
6. Replace CMOS-Battery (pain in the ***....), cleaned the Mac while doing that.

I'm out of ideas and can't find any more suggestion...

Any professionals here able to help out?

I would really appreciate it.

Thank you! :)