One slot of my RAM working other stopped working

I have Macbook Pro late 2011 edition Core i7 2.8 GHz, 8GB RAM, 13 in. My macbook suddenly started beeping on startup. I opened it and tried to check with different RAM but it still didnt work and then I took out both the RAM and used one RAM only. With this experiment I was able to find out that bottom slot has problem and top slot is working fine. Currently I am using one slot only. I just want to know whether this problem is related to slot alone or it has something else to do with like Northbridge etc. Also how can I replace the bottom RAM slot.