I built my first computer back in May and had quite a few problems at the beginning including an error code I have now. It has been working perfectly fine for about 3 months, when I turned it on this morning I received short continuous beeps for about 15 seconds then 3 short beeps at a different pitch. The error code displayed is 15 which is Pre-Memory northbridge initialization is started.When I first had this problem it had to do with the RAM, but after using different slot combinations it eventually worked. I had 2 RAMS inserted, but only 1 RAM was working/being used when my computer was running. Now I have tried inserting the RAM in almost every slot possible(by its self in each slot and then together in different slots), but it still is not working