Dark Souls 1, DS1: Prepare to Die Edition Unable to Launch. Won't Start. Stops and does nothing.

[PsionV]

The Problem: You press play, the game tries to start for 3 seconds, then does nothing and shows the play button again.

I HAVE FOUND THE SOLUTION!

Quick Way:
Go to dll-files.com, download 64 bit version of d3d9.dll and msvcr90.dll.
Go to your Dark Souls installation folder, usually
C:\Program Files (x86)\Steam\steamapps\common\Dark Souls Prepare To Die Edition\DATA
and place those two .dll files in there (replacing the existing ones) after un-archiving obvs.
Verify your game files using steam and the game should play!

Full-Proof Way:
Download Dependency Walker x64 version 2.2 if you're using Windows 10.
If you're x32 bit then you'll want to use x86 files for DS1 not x64! (x86 means 32 bit for stupid historical reasons FYI! Windows 10 is 64 bit also.)

Download here
https://www.dependencywalker.com/

Open the software, go view, check full file paths.
Click file, open, and find the DARKSOULS.exe in the file path
C:\Program Files (x86)\Steam\steamapps\common\Dark Souls Prepare To Die Edition\DATA

There will probably be a 'errors were detected' warning.
Go full screen, there's alot of data.
Go to module section and scroll down the list, there should be a lot of x64 in a column, follow this and note any x86 folders.

Go to dll-files.com and download 64bit version of all .dll files that are x86 and put it in Dark Souls 1 installation directory given above and below
C:\Program Files (x86)\Steam\steamapps\common\Dark Souls Prepare To Die Edition\DATA

If the .dll files you put in had 64 on the end (fmod_event64.dll, fmodec64.dll and steam_api64.dll) which were x86 files I found using Dependency Walker
(DW), these may not be the same as yours but don't worry. Make sure the old .dll file is deleted, and change your new fmod_event64.dll to fmod_event.dll so delete
the 64 so it has the same name (this is an example, you may not have fmod_event.dll).

Just to be sure also copy your new x64 files to
c:\windows\system32
Also make sure to remove the 64 from your .dll file names.

The DARKSOULS.exe is x86 (or 32 bit) but don't worry! Programs usually have a mixture of x86 and x64 and work fine, but for some reason it causes issues in this game!
Try replacing the d3d9.dll and msvcr90.dll 64 bit versions in the DATA folder of Dark Souls, then the system32 folder, d3d9 didn't work for me but don't worry
about that if it doesn't copy due to permission issues, the .dll files only need to be in your game folder, putting into the system32 folder is only required
if this issue is happening for all your apps.

If you open DW once you've replaced the .dll files and it has the 'errors were detected' warning still, it doesn't mean the game is broken. You can check
if you've successfully replaced the x86 .dll files with x64 ones. After they've been replaced just go to steam, verify the local files and your game should start!
(If you don't know how to verify local game files, right click Dark-souls, click properties, local files, and verify installation.)