Yafray and Blender worked once only on Linux

I downloaded boththe latest release of Blender for Linux. I untarred the Blender .tar file and then installed the RPM for Yafray.

They both worked fine the first time but the next time I started up my machine and Blender, i now can’t seem to use Yafray to render, using the render button when you click F10. I can however seem to use Yafray to render using the render viewport button on the viwprort render button.

when I do use the Render button on the F10 panel a window pops up (heading Yafray render) and nothing happens , almost as if its takeing a long time to render, but never doing anythiing. and then I end up with a black screen

It worked the very first time i installed blender and Yafray.

Surely a new default screen should show something using the Yafray renderer as default, but it just shows a black screen

What am I doing wrong?