Uploading files works but images don't show

Hey!

I’m currently working on a assignment for school, setting up a WordPress website on https://www.usabilityenkleur.nl but I’m experiencing a problem. Installation of the latest version of WP wasn’t a problem and installing themes is no problem either. Adding in media through the drag-n-drop function, FTP or the basic uploader works just fine, up untill the cropping point. When the uploader finishes cropping the image it shows up in the media library but it doesn’t show the actual image, just a broken file icon.

I already deleted all themes and plugins, re-installed WP on the server and even downgraded to version 3.7 but with no success. Does anyone know what could be the problem? Would be forever grateful if anyone could help me out here!

Regards,
Tristan van der Laan