I really think that previous posters have done a great job at describing where the spacers are, so I would definitely recommend taking a look at some of those posts, especially the one regarding "surgery."
The following picture is taken from the website and best depicts where the spacers are (if you don't even know where they are, how do you know whether or not what you're doing is working?
):
THIS PIC. It's the 12th picture down on the website. If you look closely, spacers are usually rubber and gray (though you can't really tell in this picture) and are situated above and below the pixel screen. They should be held tightly in place. Spacers usually shouldn't be moved. Make sure everything is screwed tightly in place, come to think of it. Also, make sure that none of the wires are loose/frayed because that could cause missing pixels as well (at least in my experience, it has). You may need to solder the wires if this is the case.