@sheila5 I google the problem. I found this:
“You have to make sure to not only select CUDA but also the correct video card. In the Settings in the “Cycles Compute Device” section it displays (if CUDA is selected) the available video cards. These appear to be able to be selected, so if one is selected the background gets darker. If I select my video card, the rendering device option inst grayed out anymore and the rendering process, if GPU Compute is selected, speeds up by a noticeable amount”
According to what I’ve read, in the compute devices in system under system preferences, you have your card connected to a monitor, so it should give you two drop downs, and you have to make sure you select the card that is also not using that reads (Display) at the end.
