There is a recurring error in Windows 10, the missing d3dx9 files. You are trying to launch a game, usually an old one and before starting it crashes and you get the missing d3dx9_xxxx.dll file. This file can vary depending on the Direct X file the system is trying to look for, but the core of the problem is the same, the game is trying to use an old Direct X file that is not stored in your system. This is a pretty annoying error because the default error message prompts a missing dll file but doesn't say it is a Direct X one. The fix to this solution is pretty easy and the only thing you have to do is to install an old version of the Direct X.
It doesn't matter which file is, as long as its name includes d3dx9 in the name and it is a dll, the problem is likely to be a wrong version of the Direct X installed in your system. Let's see a step by step guide on how to install Direct X 9 in your system so that you can play your old games in Windows 10.
First thing, go to the Direct X main page:
It will also offer you to install Bing Search toolbar or to use Bing as a default Search engine. I do not recommend to do so, so better uncheck that box before proceeding.
Once you download it, just execute it and don't forget to reject the Bing Bar again.
The time for the execution will be different on each computer as this program is searching for components in your computer and will download any version of Direct X if necessary. Once the installation is finished, reboot your system and you will be able to play any old games requiring Direct X 9.