I am able to reach the opening menu of the game, but not able to click on any of the buttons. This is the very, very first menu when the game starts up, with "Sandbox | Options | Exit" on one side and "Report a bug | Visit the forums" on the other. My mouse cursor is visible, but nothing happens when I click on any of the links. I am running Windows 10 on a pretty new computer with very solid internet connection. I was using a bluetooth mouse when the problem first occurred, but it also happens when no external mouse is attached.
I had this very issue when the first sandbox was released, and it was an easy fix. The only problem is that I don't remember the fix. I want to believe that it had something to do with the Video Card, and it's adjustments.
If you have a way back machine, and can search the original forums you should be able to find the answer that I was given then.