You dont have Correct Graphic Driver Installed, i had the very same problem which was only resolved with reinstalling of ubuntu 16.04 64-Bit, and verify if you had installed the correct Nvidia Driver by Navigating to System Settings > Software & Updates > Additional Drivers and check if you have GREEN CIRCLE Next to NVIDIA Corportation, I have attached mine for reference, In the meanwhile you can directly copy your Wangan folder which you have right now as it is to the newer installation, this saves time but you do need to install tty0, libs, vmware and others again for the newer installation. This will just save your pain to unpack and Copy updates and crack. Hope this helps!