Cycles does not render with GPU My blender system tab shows CAICOS in compute drop down...when i render with graphics processing unit compute.my render screen. is blank.but with CPU its rendering.I do not n have any error messages in console window.I have ATI 6490m graphics card with memory 1gb
Make sure, that you are running on newest drivers.

On linux run:
CYCLES_OPENCL_TEST=all ./blender

On windows:
set CYCLES_OPENCL_TEST=all
then run blender

Switch to cycles, go to system settings and select your graphic card.

The performance is limited and initial compiling of the kernel can take few minutes. But according to this AMD statement, there is a fix slowly coming in. No words on performance improvements though.