Error 404 on things after "/"

Hi!
I had no idea, how to describe my problem in one line ;-) Basically, if I use an URL, i got a 404. Some examples:
First, https://domain works. It calls the basic controller and method. Fine. But then it begins: All called files like /dasboard.css ends up in a 404 error. If i try to call a controller eg https://domain/controller, it also ends in 404.
Sorry for that explanation, I hope you understand my problem :-)
Thank you