Open OH and click on the cog in the top right. Then select settings and look at the devices tab. Against the image of the Rift, see if the light is green and if not what does the message say?
i had something apparently similar and the message was something about HDMI not being connected so I just carefully unplugged the HDMI cable and then plugged it back in again. The cable had been properly seated and I had power-cycled several times, but I suspect that my 970 was probably getting confused.
If it isn't the same issue, just let us know what the status message says.