I purchased the computer yesterday. The Installation of OS(Linux) did not work, so I desided to downgrade my BIOS/UEFI from 1.8. to 1.2. and hoped that would help. I read there are conflicts between newer UEFI and Linux. I downloaded the software here: ASRock > Products > Motherboard > A75M-HVS > Download. I used Instand Flash for that.

I got feedback from Instant flash, that the flashprocess was succesful and pressed enter to reboot. After reboot the screen remained black. I tried to restart several times. I removed the battery and set the jumper to reset for 5 minutes. It did not help.

What can be done instead of buying a new motherboard? :(