I had problems with Custom.exe once.
Your problem may come from that the unlumping process while leaving went differently as it is supposed to do.
As you suggest reinstall is a good idea, and I would suggest you to do in a new repertory.
You can also try to unzip custom in your current directory and replace all the files linked to the programm.
Finally you can try to fix things up manually. Unzip ohrrpgce_gorgonzonla.zip (or a night builder version if you are a programmer) cleanily in a new directory (let's called it custom 2). Don't add game files or extra txt file or extra hss files. Compare the files according to their name in each directory.
if you see files with strange names (like defpal#252.bin for example) that may be the file that prevent custom.exe from running correctly. Anyway, good luck!
Did it work before today?
If you open Task Manager after trying to run custom.exe do you see that it's running in the background? I expect so, since from the sound of it the program didn't crash. It appears that it froze when trying to initialise the SDL library, but before trying to create the window. This has nothing to do with any files that might be present or missing (unless possibly there's something wrong with your copy of SDL.dll)
If it's running in the background, you can try force-quitting it.
Does game.exe run? If so, I think the problem might go away if you restart your computer.
If nothing else works, try downloading a nightly build. Nightly builds have switched to SDL 2, which is practically a different library.
Last edited by TMC on Mon Feb 15, 2021 9:27 am, edited 1 time in total.