Replacing music with XWE

XWE corrupts the wad if you have it open both in the program and Doom Builder, generally. Go with Slade - the workflow is the same.

Ok... this should be very simple.

1. Open XWE or SLADE or whatever
2. Import your MIDI file
3. Name it the same name of the original you are replacing (i.e. NEWMIDI.mid becomes D_RUNNIN.mid)
4. Save WAD
5. Finished

You've created a .wad in Doom Builder? If so, it should be as simple as opening your .wad with XWE, importing your MIDI file and renaming it to D_RUNNIN, assuming it's map01.

Slade is better than XWE. At least Slade gets updates and doesn't corrupt wads. And you can do the same thing like importing midi and renaming it in D_RUNNIN(or in other music lump name) or adding texture packs. 

But I can never get Slade to work in the first place. There's an error message saying that a program is missing from my computer, and I can't fix it.

When Slade3 does not work correctly it is usually as a result of the missing Microsoft Visual C++ 2015 Runtime.

See the download page.

If that does not help, then SlumpED , the ancient predecessor of Slade3 is better than XWE.

When I downloaded it, I just pressed repair, and its been around %80 for the past 20 minutes.

Issues with running Slade aside, did you manage to import your MIDI in the mean time? The process is essentially the same in either program

No I have not.

Try an older version of slade. That could work.

Now when I try to start SlumpED, it says that MSVCP71.dll is missing from my computer.

I already fixed it