GPU compute grayed out In Blender The GPU-Compute button is greyed out. I have a fully updated system with a Nvidia GTX video card and the current version of blender.
http://image.prntscr.com/image/9e80916076b944f8a5cc9c6ec78a1a99.png
Go to "File"->"User Preferences" and click on the "System" tab. On the left it should say "Cycles Compute Device". On my machine (I have the same card) when I change from "None" to "CUDA" the GPU Compute rendering option stops being greyed out. If that's not your case I don't really know what the problem could be. Good luck!