Enter Reason: failed to load/verify boot images => new mainboard?

Backcamera and flash didn’t work. I opened and put the plug back.

Now the Pixel 3 starts fastboot with

Device-State: error!

Boot-slot: a

Enter Reason: failed to load/verifiy boot images

It’s impossible to start recovery mode, i think i need a new mainboard.

Where can i buy one?

Other solution?

Thanks and greets from germany with broken english :)