I am been having a hard time getting memory to upgrade a series of Gateway SX2800-7 's
I have had best success with Kingston KHX1333C7D3K2/4GX memory. But some work; some don't. I finally noticed that the wiring diagrams on the actual circuit boards of the memory is different. There are two different distinct patterns. One always works; one never does. With heat-sinks on, it is hard to see totally but it appears that the ones that work have the pins directly to the right of the key-notch slot on the front have wiring going to them. The ones that do not work, don't have that.
They are the same model number but in volume I find some that work (with the wiring one way) and others that don't (with the wiring the other way). Unfortunately you can't tell when buying; it is order and open and if wrong then return. I can now tell whether memory will work just by looking at circuit board.