I've bben playing FO3 fine until I had to reinstall Win10, and now a system error tells me that ' d3dx9_38.dll ' is missing?

FIXED
By using the verify/repair option.

Just for reference, the 'd3dx9_38.dll is missing' error a sign that your DirectX is incomplete.

Add this:

https://www.microsoft.com/en-us/download/details.aspx?id=19743

They did something funky with dx9 and it;s in 2 parts

Hope this helps anyone who comes by.