I Just ticked the "World Background" box and now everything shows up. [![enter image description here][1]][1][![enter image description here][2]][2]in the third picture, i loaded factory settings and now everything is ok. but if i restore the program i will loose all my configurations. I will try to export them, reinstall blender and load them again.[![second picture][3]][3]as you can see in the second picture once again the world environment is completely black. nodes are shown. thanks!
Tnanks so much for your help in advance.
[![how to turn world to white colour][4]][4]


 [1]: https://i.sstatic.net/I9d0D.jpg
 [2]: https://i.sstatic.net/pNPg8.jpg
 [3]: https://i.sstatic.net/Gx4FL.jpg
 [4]: https://i.sstatic.net/5eHvw.jpg