Slitherine

I have been playing multiplayer only, but decided to play single. When I click on single player nothing happens game still works with multi just no go in single...whats up?

Rename the folder Order of Battle - Pacific as _Order of Battle - Pacific in the Windows documents folder at:
....\Documents\My Games

Start the game and check if the issue persists.

Now that works. It has however caused anther problem. Two of the custom scenarios in multiplayer show that I do not have scenarios installed , I have downloaded both and added them to the game. However both still show as not being there....

Multiplayer maps need to go in <My Docs>/My Games/Order of Battle Pacific/Scenarios.

If you renamed the original folder as suggested by Paulo, compare the renamed and new scenario folder to see if the names of your multiplayer maps in there are identical.

Can I or should I have deleted the folder I renamed?

If you don't mind to loose any saved games, you can delete that folder.
But before this check what adherbal told you to do.

I did that. All looks the same now. I moved scenarios so each has the same scenarios. What I am concerned about is the coming upgrade. Will it upgrade both folders?

If you have already transferred you can delete the other folder.
The game will only store data in Order of Battle - Pacific.