I have made a project with target spot light's and it's volume light (to see only the long light ray). All was ok, but... I don't remember what I did in the last project, but now in a new one, when I place a target spot light, the entire project is in shades and the light ray can only be seen :S. I have to place a "omni" light to see everything while I'm editing.
Is there some way to use the target spot light without shadows? (I only want to see the light ray) :S
I think it has to do with the "exclude" button just to the right below the uppermost light settings. As I remember, to get Volumetric lighting, you have to either turn of shadows or lighting in the menu that comes up with exclude. Try switching one of those choices on or off, and see if it helps.
You may also want to check out the Attenuation settings; they may be set so that the light never reaches its' target. Also check the intensity of the light, in both the light and in the Global Settings. There may be something going on there. Good luck! There are lots of things that can cause a problem - you might also try a New File, and then Reset - that may help you out.