Firstly, i booted f8 bios then I tested each rams with memtest86 v4.00 and both passed @1600mhz and 1.7v (4 times). However, when i used them together there were some errors @ 1600mhz or 1333mhz, from 1.7v to 1.9v. I can use the first ram(1.7v or 1.9v, 1600mhz) perfectly if i use only it . And interestingly, when i used only the second ram (@1333mhz or 1600mhz) win7 or ubuntu 10.04 could not be booted even the ram passed the test. There is something wrong and i don't know what it is. So any suggestions?