Client fails to display graphics, everything else works

Hello! My friend floddertje2 asked me to help him with his League of Legends installation. He has reinstalled the client several times and followed the instructions from a support agent, who sent him an alternative installation method, multiple times, to perfection.

I viewed his laptop through TeamViewer, which allows me to see and control his laptop remotely. He is running windows 10, and the problem started occuring since the latest feature update. I assume it's the same update that I installed on the 16th, but League is working fine for me. It's windows 10 version 1803.

The problem is that the graphics for the UI of the client are not displaying. What you see is a box in the top left that looks like this: https://i.imgur.com/M8bDHqS.png The box will move around if you drag the area on the same level of that box, so I assumed that is the top of the window. It doesn't work to the left of the box, so it's the top left corner. I overlayed my client so I can see where everything should be, and since sounds are working, I can confirm that we successfully logged in without any graphical feedback. After that, the league client started patching, or so we assume, as Task Manager showed that it started downloading and writing to the disk. After some time, we heard the sound that the client always makes when it finishes patching.

So, controls and sounds/music are working, but graphics of the user interface are not. Does anyone know what could be causing this? If you need any more details, do not hesitate to ask.

EDIT: One of the first things I checked is the log files when launching the client. While I cannot understand everything in there, I did not see anything that would clearly indicate an error such as a missing dependency/library like vc redist or .net framework.

Greetings, Difensick