I have just installed vagrant box with command:
vagrant init ubuntu/xenial64
and the booted it up with:
vagrant up --provider v
You could try installing the vbguest addition plugin, and see if that helps.
$ vagrant plugin install vagrant-vbguest
vb-guest plugin repo
Also, sometimes when you install the vbox on your computer if you dont give permissions to the additional drivers that it wants to install it will not function properly. You might need to re install to make sure that you accept the prompt when asking to install some drivers.
In case none of this works, you might try to boot withouth a gui, and paste here the output when trying to start the vagrant machine.