sis m671dx

I have a notebook ASUS x59sl with chipset SIS M671DX, evrithing is working OK, but it hase slite problem whit the memory. It is working as DDR2 on 667mh, but i have two ddr slots with 11g and 12g, i think that it shuld work as DUAL DDR, i tried with two same memoris KINGSTON 2*2 Gb and i hade the same result.

Can any one halp me:(