Stop npp and make sure no other instance is running
rename %appdata\notepad++% temporarily
start npp - a new notepad++ directory should be created with all the default settings.

I deleted the config file from the Appdata folder (because i didn’t have it in the installion folder) but that neither changed anything, as i previously said. I previously used the 7.5.2 build (which is back from november 2017 if i’m right) and right now i’m using the most recent stable version. I will provide you two pictures about the current default color theme:

and the one which i want to use in every document:

look in the style configuration but that doesn’t change anything.

looking won’t change anything. what settings did you change in the style configuration? how did you expect it to affect your display, and how did it actually affect your display?

Deleting the config file does nothing either

It does do something: it makes Notepad++ regenerate to the default config. But only if you delete the right one. Notice that @Ekopalypse mentioned two possible locations; you didn’t tell us which you deleted… some of the requests below will help us narrow in on whether you chose the right location.

Any more advice?

Please give us more information.

What version did you used to use? What version did you upgrade to? => ? menu, debug info from the new version would be helpful – this will also tell us whether you should have deleted the AppData or the one in the exe’s folder) edit: finish that sentence; also => do you have Settings>Prefences>Cloud enabled?) /end edit

What theme did you have selected before? What theme do you have selected now? => Settings > Style Configurator, hit Alt+PrintScreen, and paste the image in your reply.

In the old version, had you customized any of the Style Configurator settings? If so, did you make those same customizations?

Do you have a screenshot of what you mean by “yellow line marker”?

in order to reset everything to default configuration, delete the config.xml file.
Depending on your installation, this file is either the one under %appdata\notepad++% or the one in the directory where your
notepad++.exe is.