I am trying to install Ubuntu 18.04 LTS on my computer (Deskmini, Ryzen 3200G), but when I get a black screen after going past grub. Adding nomodeset doesn't change anything. Can anyone help?
18.04 LTS images use kernel 4.15, but support for the 3200G wasn't added until kernel 5.0.15, or 5.0.0-21.22 in Ubuntu, so you need to install linux-image-generic-hwe-18.04 after you get the installed system booted, or just install from a 18.04.3 or later LTS image. You did not say whether your boot failure was on booting the installer, or booting the freshly installed system. If the former, make sure you are putting "nomodeset" in the correct place in grub. I was able to boot an 18.04 disc on a 3200G (non-A300) that way. If that does not work for you, then there may be additional things your particular motherboard needs in grub, possibly "iommu=soft".