I have had a lot of calls on Civil 3D taking forever to open, and there is finally a fix. You will have to follow the directions from here. Once you have followed the instructions, open the problematic drawing. It will still take forever to open. However, once it’s opened and saved, the problem goes away.
Thank you to Steve Hill at Red Transit Consultants for reminding me to edit this post.
Make sure you do this on ALL machines. Otherwise the issue will keep reoccurring.
Take a stop over at Red Transit Consultants if you are interested in some awesome add-on tools for Civil 3D, Map 3D, AutoCAD, and much more.