A lot of good folks on this forum use KDE. Not me. I guess it is pretty and all that, but I stick with XFCE. Simple but nice. There may be good reason to use KDE, but its not much use to me, best I can tell.
Something is probably wrong with your video settings. I can't recall just what to do, but you are right to come in via the TUI and then go to xorg or xconf or some such and select different video settings.
Welcome to the forum. It has folks like me, who know little about the tech stuff and a lot of folks, like hata_ph who know the tech stuff. Respond to hata_ph's suggestions. He will get you fixed up.