Black screen when assembling ASUS and AMD [solved]

I just was assembling a 8 Core system with 6 SSD RAID slots.

• Motherboard ASUS B450M-A II
• CPU: AMD Ryzen 7 5700G Tray AM4 8×3,80GHz Radeon Graphics

When starting the system i received as blank screen, but everything else seemed to work fine.

The mouse appeared not to give any signal but USB Memory stick did.

When shutting down the system but leaving the power on I pressed the Flash Back Button on the back of the board for three seconds. It gave me the right feedack and the LED close to the Button was flashing.

So this led me to the conclusion that the motherboard was working.

I removed the memories from Channel A2* and B2* as it is written in the instruction and put only a single memory on Channel B2 *.

Same isse.

Then I placed the memory on channel A1 and the system started.

So I noticed that the channel B was not working.

I decided to remove the CPU once again and checked the pins.

Seems there was a bit of thermal paste on the pins top left side. It could have been the cause. I removed everything carefully with a cotton swap.

After putting the CPU back into the Socket gently everything worked nicely. 🤩