I downloaded an experimental build of blender from june 30th. i opened a scene in blender, with blender materials. then i switched to the yafaray rendere,(i wanted to port the materials to yafaray). but then my computer started laggin as hell.
couldn’t move my mouse, only an inch every 5 seconds,
i reboot my computer, but now the blender console crashes at startup. reinstalled 2 times
Help 
EDIT:
The scene didn’t have many faces in it, it didn’t lag in the viewport (before i switched)
EDIT:
Console says :
Info : Config directory with “startup.blend” file not found