Your CPU cooler is covering your RAM slot, right?
You can try the other slots. You should use 2 & 4 (which should be the same color) if you want to RAM to run in dual channel mode. You may have trouble overclocking (CPU or RAM) if you use the 2,4 configuration. It may be totally fine.
You could try to carefully bend the RAM heatsinks so that they do not touch your cpu cooler. What cooler do you have?