Hi,
This is strange. I had VirtualBox 5.0 (not sure of the release number) running on an old Windows 7 laptop with a Windows 10 Guest. I had both 2D and 3D acceleration enabled under Settings - Display.
Yesterday I switched laptops and moved my VM to a new Windows 7 laptop. I did not have the installer so I downloaded the new latest VB installer. I chose the latest stable installer from the downloads page which is: VirtualBox-5.0.2-102096-Win.
However, on starting my guest, I only saw a solid color screen. When I interact with it, I see dark boxes. Since I know Windows 10 guests are not officially supported, I downloaded the latest nightly build. Which happens to be a LOWER version number: VirtualBox-5.0.1-102010-Win. However, the problem was still the same. This is the build I am currently running along with the same guest additions.
On googling, I found a blog comment that talked about disabling 3D acceleration and sure enough, the guest machine becomes usable then. The comment, mentions uninstalling and reinstalling Guest Additions in 3D mode with Windows 8 compatibility checked and doing that did NOT fix the problem for me.
I am currently running the guest with 2D acceleration only. I am hoping that in a few weeks, someone will fix the issue and so I will try upgrading to the latest in a few weeks. Is there any other suggestion anyone has for me?