Viewport Background not showing....help needed

[danb4026]

Not sure whether this should be in this forum or Vray's (because I use Vray).

 

But for some reason, I cannot get the viewport background to show. I have an HDRI in the environment slot (both max's and vray overide's), I have "use environment background" checked. I configured the viewports to "show background". I have done this a thousand times before without issue.

 

I upgraded my graphics card recently (GTX 580), perhaps that's the culprit? Drivers seem to be all up to date.

 

Any ideas? Probably something really stupid.