We occasionally see reports where AutoCAD Civil 3D opens and then immediately closes with no message displayed. Typically, the described behavior could be happening when the program is not able to get its license; but there may be some other reasons for it. After you have confirmed that program in fact is able to ping your license server (if network) and that your license is valid it’s time to look somewhere else. In the next few paragraphs I tried to highlight a few places where you should look for clues. There are more, I guess, but these are most commonones I am aware of.