1 - open steam and make sure you have fallout 3 (goty counts as well) and right click on its icon

2 - go manage and browse files and right click on fallout3.exe (side note: you must do this to fallout3launcher.exe as well)

3 - go properties then click compatibility, select "run this program in compatibility mode" then select "windows 7"

4 - once done right click on fallout3.exe and click "run as administrator" (same goes for fallout3launcher.exe)
(side note: this will open fallout 3, you must close it as soon as you get the chance)

5 - afterward download the file in the link below and open up a second file explorer tab
(side note: account creation will be needed)

6 - Once the file is downloaded unzip it and you should see d3d9.dll, keep that tab open

6 - keeping the fallout 3 folder open (the one with fallout3.exe) on the second tab grab d3d9.dll and drag over the file to the folder
(***IMPORTANT NOTE, MUST READ***: make sure when moving it the file says "move to" not "open with", this can cause serious problems if done incorrectly)

7 - close both folders and go back to steam, launch fallout 3, and if you've done all the instructions correctly fallout 3 will open and run perfectly

Thanks for reading, and i hope this works out for you.

(Link: https://www.nexusmods.com/fallout3/mods/17209?tab=files&file_id=82734)