Same steps are valid for C&C Generals: Zero Hour too, but, before running Zero Hour, be sure C&C Generals is running well and be sure C&C Generals is installed before Generals: Zero Hour.

1) Download DirectX 9.0 from here https://www.microsoft.com/en-us/download/details.aspx?id=8109
2) Click on directx_Jun2010_redist.exe and it'll ask you a folder.
3) Pick any folder to extract the packages.
4) Open the folder that you picked.
5) Find DXSETUP.exe and run it, and complete the setup.
6) Run the game.

1) Find Generals in your game library.
2) Right click on Generals and go to the properties.
3) Find the title "LAUNCH OPTIONS" and the input below of it.
4) Copy and paste this without quotes to the input: "-xres 1920 -yres 1080"
5) Now, you are able to play Generals in 1080p (FHD).
6) If you have different resolutions rather than 1080p, you can just edit by according to it like: "-xres 1366 -yres 768"

I haven't run into any compatibility problem with Generals in Windows 10, but some people may run into different problems.

(For example, I have run into FPS Drop problem in campaign mode of Generals: Zero Hour due to the compatibility issues, but I haven't run into in Generals.)

Changing compatibility mode sometimes works to solve these weird issues, here are the steps:

1) Right click to the C&C: Generals in your Steam Library.
2) Click on Properties in the right click menu.
3) Select installed files from the tab.
4) Click on Browse button and it opens the folder of the game.
5) Find Generals.exe and right click to it.
6) Click on Properties.
7) In the tabs, select Compatibility.
8) There's a section named "Compatibility Mode" and underneath of it there's a checkbox with a title written "Run this program in compatibility mode for: ".
9) Click on this checkbox.
10) Now, the selectbox is opened. Select "Windows XP (Service Pack 3)" and click Apply.
11) Run the game.

This problem is based on the 'replay' files, in this section, we're going to solve this problem by a simple solution.

1) Find the save data in below paths.

for Generals: C:\Users\{YOUR_USERNAME}\Documents\Command and Conquer Generals Data

for Zero Hour: C:\Users\{YOUR_USERNAME}\Documents\Command and Conquer Generals Zero Hour Data

2) Right click on Replays folder, then click on the Properties option.

3) You'll be seeing Properties of Replays folder, click on Security tab.

4) There'll be some user groups or users like SYSTEM, Administrators, {YOUR_USERNAME}

5) For each user and user group, click on Edit and click on a checkbox under Deny for only Write permission.

6) Then click on Apply, and OK and enjoy your game.

Note: Twilight Flame map might still be laggy with 7 bot players, but other maps are fine with 7 bot players with this solution.

I've run into this problem recently and I think I found the reason of this issue.

I have 2 monitors and these monitors have different resolutions. If I set a resolution that is not supported by the active monitor, then game throws this error.

Basically, you can NOT set a resolution that your monitor does not support.

For example, if your notebook have 1366x768 max resolution and you set 1920x1080 resolution for the game somewhere (in options.ini, in Steam Launch Options or somewhere else), game will throw this error.

Here's a quick look how to fix this:

1) First of all, be sure you have installed DirectX as I mentioned in Problem 1. Please read carefully, and follow all the steps.

2) Most of the people override their game configs or game launch options somewhere to run this game, you should revert these changes.

Note: Uninstalling and/or reinstalling the game won't revert all of your changes. You need to check if there's an entry related to screen resolution in options.ini file (and the other config files if you changed or used 3rd party tools).

In options.ini, if you've defined resolution somehow then you'll see something like this below.

Resolution = 1920 1080

You should be sure that if your screen resolution is the same with this resolution. If you have 1366x768 resolution, then you should change this to below.

Resolution = 1366 768

You can find the options.ini file in below paths

Zero Hour: C:\Users\{YOUR_USERNAME}\Documents\Command and Conquer Generals Zero Hour Data

Generals: C:\Users\{YOUR_USERNAME}\Documents\Command and Conquer Generals Data

3) If you haven't changed anything in config files before, then you should check your launch options. You can follow the steps in Problem 2.

4) If you set resolution in options.ini and also in Steam Launch Options in the same time and if these resolutions are different than each other, remove one of them or make them same.

A lot of people said deleting dbghelp.dll in the game folder works (for both Generals and Zero Hour). I haven't tried that, because I solved my problems with the steps I specified above but some people ran their game by deleting this file.

Note: This method is not tested by me, however I am sharing this here. Maybe it works on someone else's PC too.

Same steps are valid for C&C Generals: Zero Hour too, but be sure C&C Generals is running well and be sure C&C Generals is installed before Generals: Zero Hour.

Hopefully, this guide helped to solve your problems.

Good luck, have fun!