Since you're an Admin on the machine, there's nothing that needs to be done in the registry.
Originally, I was going to have you right-click each of the registry hives and choose Permissions. Within the permissions area, add your account and allocate full rights.
However, since you already have Admin rights, there could be an AutoCAD profile issue. To reset your profile, perform the following:
Browse the registry and delete the following folder:
Browse windows explorer and delete the following:
Once these folders are deleted, start Civil 3D 2012 and those files (Autodesk Profile) will be recreated.
Let me know if this works.
If you're running Windows 7, disable the UAC...
Go to the start menu, and type UAC in the search box then hit Enter. Slide the bar all the way to the bottom and reboot your system.
If this doesn't resolve the issue, browse to the following location and delete all of the files beginning with "adskflex_":
Windows 7 directory:
Windows XP directory:
Start with some of our most frequented solutions or visit the Installation and Licensing Forum to get help installing your software.