|The memory is not only of different sizes, but also different speeds. This will sometimes work with the slower memory in the first slot, but not the faster memory in the first slot so try switching them. If that does not work then the timings on them are too different to work together, especially on that board. Either use the 2GB stick by itself, of purchase a stick that matches it. If your OS is 32bit, and you install 4GB of memory, it will only recognize a little over 3GB of it, but it will work, so if you get a good buy on a matching 2GB stick, buy it. If the memory is not the same brand and model, it needs to be the same speed and use the same timings (can be listed like: 6-6-6-18 or similar) to run well and is best if they are listed on your motherboard's RAM compatibility list (already tested to work with your board).|
You have to be a little bit crazy to keep you from going insane.