Do you mean the html block? Where exactly are you putting the block - on a course page? On a quiz page?
Have you edited the default roles? By default, all roles can see blocks anyway. Have you overridden the roles anywhere?
Can you post screenshots?
(Ich spreche Deutsch) Textblock is German for HTML block and Test is German for Quiz so I think perhaps you need to look at Darstellungen (Appearance) and check that it displays or doesn't display HTML blocks (Blöcke bei den Testversuchen zeigen)