Sorry if I make some mistakes in the text but I'm Italian. I've installed Windows NT 3.51 both in VirtualBox and in VMWare and there was no way to install the video drivers. Every time I installed and restarted the virtual machine, a black screen appears after starting the operating system. I followed several videos on YouTube and tried to search on the internet but nothing. Can someone help me???

Just use 86box and you'll be fine with the video drivers.

Under VirtualBox you can just use the boxvideo.sys video driver and it works perfectly fine if you copy framebuf.dll from the Windows NT 3.51 CD beforehand (it doesn't get installed automatically).

And which drivers are you installing? I have VM with VBEMP NT driver and it works fine.