Rendering issue regarding Vray for Rhino

Hi.I have an issue regarding rendering using vray for rhino. Once done and when clicked the render option,the render command appears but the render window does not appear.Please help.I have provided below what it looks like.what should I do??

To show the last render you should click the _VFBFrameBuffer tool.
Is the last button on top of the Vray options Windows (the rectangular one).
But you need to do 1 render at least.

-R-

Its not the last render. After “clicking” the render button nothing appears. The window is not opening. What to do??

If you add a material to material list, do you get a preview rendered?