Problem with opencl - AMD Radeon R7 370 4GB

Hi guys, first, sorry for my english im from chile

well, as the title says, when i rendering anything, even a bucket, the final render is gray or black

depending on the color display more.

I did all the normal, change in user preferences to opencl, and shows me alone “Pitcairn” and choose,

then in device selected: GPU Computer, also changed to experimental, and still rendering in gray or black

mi pc specs is:

proc: i7
mother: asus hb1m-k
ram: 8
vgraph: Sapphire® Video AMD Radeon R7 370 4GB GDDR5 NITRO DUAL-X Cooling

Thank you very much from now :o