i have a stable running computer, and one day my computer would not boot up. the motherboard showed error code 55, and google said it was a memory code. so i pulled out the older of my 2 pairs of ram sticks. and tried getting my computer to start up. after some rearranging, and a few tries where the power would continuously cycle on and off for about 1 second. i managed to get my computer to boot up again with memory installed in slots B1 and B2. i thought maybe just my memory was bad, so i purchased an identical pair of ram as the working pair and my computer went back to the error code 55. swapping them with the working pair, and only populating B1 and B2 my computer started, but would not start with A1 and A2 populated--either alone or with B1 and B2. long story longer, i can get my computer started with the b slots, but it will not start with anything in the a-slots. the only thing i could find is something about a cooler installed, but my cpu only uses the plastic tabs for the fan.