If you have just installed KDE neon or another Ubuntu 18.04 based operating system and after installation it has booted to a blank screen with a cursor then it might be because it is trying to boot another UEFI system.
This happened to me today and it wasn't until after I had reinstalled the operating system that I thought to check whether the UEFI settings in bios were interfering with the boot process. It was actually fairly easy to diagnose as it is a Dell laptop and the F12 boot menu shows you the UEFI default boot loader.
If that is the problem then you should be able to change the default loader in the BIOS and delete the cached one if needed. I am not actually sure whether the problem is the BIOS caching it on the motherboard or the old folder in the /boot/efi/EFI directory. On mine there is an Ubuntu folder in the /boot/efi/EFI directory but as I don't have another one around to look at at the moment I can't say whether that is normal or whether the /boot/efi partition was not deleted at installation.