My recomendations: Copy all the saves, techs, and everything you care about to a safe folder (if you have a USB drive, copy the files in it AS WELL as the folder in your computer) Then, delete the game from steam. After it deleted, go to steam folder, delete all the remaining files. Also check AppData for payload studios folder. Now, reboot your system, and install the game again. If doesnt work, it might be a hard drive issue. Try installing the game to a diffirent hard drive, or USB drive (if you have one). If it fixes the problem, then it was the hard drive. If it doesnt, it might be this
all the hardware I own went bad all at once
Also, if you are using older version of Windows (xp, vista, 7), your operting system might not be supported by newer versions of unity. But it is not likely to be true