virtualbox.org

I did a fresh installation and it works now.
My mistake was arround grub installation that I did manually instead of the automatic one that was not proposed by default.

Setting memory to arround 8GB and VRAM to 128MB doesn't fix the issue.

I'm using Virtual Box 5.2.22 r126460 on macOS Mojave 10.14.2.

When I launch Debian 9.6.0 amd64 I got a black screen with a cursor blinking.

I can't figure out how to fix it.
I have no 2D or 3D acceleration enabled.