OK, did you just move the stick from #3 to #1? Try moving #2 to #1 slot and #3 to #2 slot. In other words, try reversing the sticks. If that doesn't work, put them back the way you started and just remember that old saying, "if it ain't broke, don't fix it!" Seriously, if reversing them doesnt' work, you may indeed have a bad slot. But that is fairly rare. I would also be out of options. Is all the RAM in spec for your system? Are all the settings in your BIOS for the RAM correct? What does your configuration show during boot for the RAM? Usually there is a box that will have a listing of RAM in "Slots 1,2". Maybe others will have different ideas.