If you are having problems running Stronghold 3 please follow these troubleshooting steps before contacting support...

1) Make sure you have installed the prerequisite files required to run Stronghold 3
This should happen when you first run the game through Steam but sometimes they may not get installed, especially if you have updated the old version from the Stronghold Collection.
*
Latest DirectX files:
C:\Program Files (x86)\Steam\steamapps\common\Stronghold3\resources\directx\DXSETUP.exe *
or
http://www.microsoft.com/en-gb/download/details.aspx?id=35
*
Microsoft Visual C++ 2005 SP1 Redistributable Package
C:\Program Files (x86)\Steam\steamapps\common\Stronghold3\resources\redist\vcredist_x86.exe *
*
Microsoft Visual C++ 2008 Redistributable Package
C:\Program Files (x86)\Steam\steamapps\common\Stronghold3\resources\redist\vcredist_2008_x86.exe *
*
Microsoft Visual C++ 2010 Service Pack 1 Redistributable Package (MFC Security Update):
C:\Program Files (x86)\Steam\steamapps\common\Stronghold3\resources\redist\vcredist_2010_x86.exe *
or
http://www.microsoft.com/en-gb/download/details.aspx?id=26999 (download the vcredist_x86.exe file)

2) Verify your Stronghold 3 files

Login to the Steam client
Within Library, right-click on Stronghold 3 and select Properties
Select the Local Files tab and click the Verify Integrity of Game Cache button.
Steam will check all the game files were downloaded correctly. This process may take several minutes. If any files are missing Steam will download them the next time you run the game.

3. Delete your Stronghold 3 Settings file
There is a chance your graphics settings could be preventing the game from running correctly.  Locate your C:\Users\[User]\Documents\Stronghold 3\Profiles folder and delete options.xml.  This will force Stronghold 3 to redetect your computer settings again when loading the game.

4. Delete your Stronghold 3 profile
There is a chance your Stronghold 3 user folder is corrupt.  Locate your C:\Users\[User]\Documents and rename your Stronghold 3 folder to "Stronghold 3 Old".  When you next run the game a new Stronghold 3 profile folder will be created.
If you do need to rename this folder to get the game working, your old saves and campaign progress won't appear in game. Don't worry, they are backed up in the folder that you renamed, and we can help you restore them.

5. Create a new Stronghold 3 profile location

Some problems can be caused by your computer not being able to read or write to the default profile directory.  In order to workaround this problem we have created a system to manually set a new profile directory path.

To change the profile directory path edit the options_override.xml file in C:\Program Files (x86)\Steam\steamapps\common\Stronghold 3, or within located within your own custom installed directory.
The file contains a single parameter: <override user_data_path="" />
To change the directory, edit the file so that the path to the new directory in which you want to save is between the quotations.  When using this option, a new "Stronghold 3" directory will be created in the directory specified i.e. if you specify "c:\users\documents\games" then the game will create a "c:\users\documents\games\Stronghold 3" directory if it doesn't already exist.
WARNING: Be very careful! The game will attempt to read and write files from the specified directory. Use at your own risk! 

To use the default directory, leave it blank or delete the options_override.xml file
PLEASE NOTE: Steam Cloud will NOT work if you use an override path. Steam Cloud only works with the Documents\Stronghold 3 folder.

6. Do you have an anti-virus program installed on your computer?
Lots of games have problems with overprotective anti-virus programs.  If you are using anti-virus please make sure Stronghold 3 has been added to your list of exceptions.  Please consult your anti-virus manual for instructions on how to do this.  The default installation path for the Stronghold 3 game file is C:\Program Files (x86)\Steam\Steamapps\common\Stronghold 3\Stronghold2.exe

7. Use the Windows System File Checker tool to repair missing or corrupted Windows system files
System File Checker is a utility in Windows that allows users to scan for corruptions in Windows system files and restore corrupted files. This article describes how to run the System File Checker tool (SFC.exe) to scan your system files and to repair missing or corrupted system files.
https://support.microsoft.com/en-gb/kb/929833

8. If you can't load the launcher, try loading the game directly
Before loading the game the Firefly Launcher should appear.  If the launcher is not appearing then you can load Stronghold 3 directly by browsing to C:\Program Files (x86)\Steam\Steamapps\common\Stronghold 3 and running Stronghold2.exe *

9. Create a new local user account
Some errors occur because of a problem with the current Windows local user account.  Create a new local user account using the following instructions:
https://support.microsoft.com/en-gb/instantanswers/5de907f1-f8ba-4fd9-a89d-efd23fee918c/create-a-local-user-account-in-windows-10
Run Stronghold 3 in the new local user account.
11) Delete files: msvcp100.dll and msvcr100.dll

Try deleting msvcp100.dll and msvcr100.dll files from the game folder (C:\Program Files (x86)\Steam\steamapps\common\Stronghold 3) and run the game.

* - this is the default Steam install location for Stronghold 3

If you are still experiencing problems, please contact support with the following information:
1. A detailed description of the problem
2. A list of any security systems on your computer including anti-virus software
3. A dxdiag file from your computer so that we can view your computer spec

We have provide the steps on how your get your DxDiag file
1. Click on the Windows search bar
2. Type and select dxdiag
3. In dxdiag - Click on Save All Information
4. Save the dxdiag.txt file
5. Use the Contact Us form, select Choose Files add the dxdiag file