PLEASE HELP MEEEEE! I'm stuck in the Material room. 

After three hours spent creating a figure which looks perfect in preview, every time I render it in the Material Room it goes to a barely defined yellow sillhouette. I've disconnected all the nodes and tried to start from scratch - but the render still blasts all the detail.

Is there a magic button somewhere called WYSIWYG which realigns all Material Room parameters to erase all the mistakes I MIGHT have made and makes the render look like the preview?????

Infinite thanks for any help provided......