Oliver Ballerdale wrote:I tried to redownload GZDOOM the usual way from the official page ......
Oh, so many questions we need the answers to, to be able to help you.
What do you mean by trying to redownload GZDoom? Did it download or not?
Which version of GZDoom, x86 or x64? Which version number?
If you were able to download it, where did you install it?
When you say redownloading, did a GZDoom version run successfully before that?
Did you copy DOOM2.wad into the install folder?
As _mental mentioned the graphics hardware.
Are you sure that your graphics card can handle OpenGL 3.3 and higher or Vulkan for hardware rendering, Direct3D 9 or later for software rendering?