There is a new update out there so now is as good a time as any to post something about reinstalling Civil 3D. Occasionally, stuff happens that defies explanation and finding anything resembling a reasonable direction can be a challenge. I know this is true. It has happened to me.
Often, a quick and easy solution is to simply reinstall the program. As is often the case, there is a right way and a wrong way. Fortunately, Autodesk has published the steps necessary to perform a clean installation and everybody knows a clean installation is a happy installation!