Gpu render with GForce 105M help

My old notebook has a graphite card Gforce 105m. It seems that blender can recognize it but the rendering results with gpu is quite different from cpu rendering.
btw, I am just following the great Andrew Price’s video about making metallic text using cycles render.

rendered by cpu

rendered by gpu, everything else are the same and I just changed render device from cpu to gpu.

Is it because of my old graphite card? any clues?