Blender doesn't render Cycles with GPU? I was messing around with effect and when I went to start a brand new scene to render something that doesn't use effects nothing shows up until I switch render with CPU?
As of now, you need a CUDA capable card in order to leverage GPU renders reliably.  OpenSL for AMD cards are hit or miss right now.  The rendering guide also suggests that your card may not have enough memory.  

https://www.blender.org/manual/render/cycles/gpu_rendering.html