The clip and project monitor shows the correct frames when scrolling through a clip or project.
However, when a clip or a project is played the clip- and project monitor stay black, although the audio is played.
The graphic card may not support hardware acceleration.
Disable use of hardware acceleration in Kdenlive settings. Look for the video driver used by SDL and try changing to x11 or to xvideo and see if it works. You need to restart Kdenlive after that change.