I have blender 2.75a and AMD Radeon HD6850 gpu. But when i go to user settings and there system. There i changed it to OpenCL and Barts. And to Cycles Render and then on render menu from cpu to gpu compete. And then i try to render my scene. It just stops working, i see that grey chess pattern. Nothing happens and then crash. It doesnt matter if i have one cube in scene or 100 cubes. Same happens with Rendered Shading on.
OpenCL is supported for GPU rendering with AMD graphics cards. We only support graphics cards with GCN architecture (HD 7xxx and above). Not all HD 7xxx cards are GCN cards though, you can check if your card is here.
oh well i guess my graphics card isnt good enough