Host: AMD Phenom 2 x6 1055T, 4 GB RAM, GTX 550 Ti with driver version 384.90, Ubuntu Mate 16.04.3. VirtualBox 5.2.2 from official site;
Guest: WIndows 10.
Situation: if I run VBox WITHOUT guest additions (GA), all working nice (excluding sharing folders between host and guest). Once I install GA, the Launcher window gets all black. When I uninstall GA, all works again.
I have a suspicion that this is a known issue with VirtualBox. To confirm, can you disable 3D acceleration to see if that fixes the issue you are seeing?