If not working, we can test in Safe Mode:
If still not working, the wifi antenna board is faulted. You will have to bring to a local Apple store or Apple repair shop to have it replaced. Usually it will cost about $80 for parts and labor.
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Where is the battery?
Unfortunately these are the efforts we have already tried. I listed in my question that I had tried to make the wi-fi connection inactive. I would like to add new copy of my wi-fi connection, but do not know how to do this. I have seen on apple discussion boards that this is a software issue with the 10.8.5 Mountain Lion---not a hardware issue. How can I add a new copy of the wi-fi connection under settings?