I'll try to make this short, but need to give all the details, so...... i have basically a gaming system for my wife. Built it for xmas and because i went high end with video card, i only got 2 gigs RAM. For these few months, system has been ROCK SOLID, never a crash, fast as fast......everything great. Found RAM, same type i have in, had rebate going so i picked up another 2 gigs.Shortly after install, system would kick out of WOW and back to desktop, giving memory error. You could always relaunch without reboot and launch WOW again till it happened again. Pulled new 2 gigs and system went back to flawless operations. Downloaded free memory tester (http://www.memtest86.com/) and did some testing. I decided to do a baseline test using only known good 2 gigs ram. Test fails hard and locks up system.Move 64k block test. And this was with first 2 gigs ram that works without errors.Swapped ram with new, was able to quickly isolate one defective chip, other seems good. NOW back to old ram that works flawless, installing both sticks, tests fails as stated above.BUT, if i take system down to 1, 1 gig stick and test one at a time, both sticks pass, without a problem, multiple tests. IF i move one of these sticks to memory slot 1 instead of zero, they still test fine. Only when both sticks are in does memory test fail. ANd now as i writing, wife informs me my flawless system just rebooted on it own, FIRST failure every. This is 1st ram, so i just swapped slots, but not ram. Moved ram in slot 0 to slot 1 and vise visa. SEEMS to be doing okay. someone got some idea's??