Alex29 thanks a lot for contacting us. Regarding your issue, for me it looks like you have a problem with your monitor. I would recommend you add a second monitor, connecting the motherboard through DVI-I port or display port.
If you got the same image on both monitors, please go ahead and replace the motherboard. If the image is fine on the 2nd monitor, you would need to replace the Dell U2412M monitor.
Thank you for getting back to me.
I tested with an old Sony 1024x768 monitor and there were no issues.
However the monitor that shows problems with the motherboard is a Dell 1920x1200, aspect 16:10.
As the Dell didn't have issues with a few different motherboards it looks like DH87RL just cannot handle this resolution/aspect ratio correctly during POST. Maybe a fix in the future BIOS release?