The power source for my eight month old MacBook Pro isn't working. It is one of those magnetic plugs that attaches to the MacBook port at the side, back on the left. There are no lights saying that it is connected, neither green nor brown. I plugged it in last night and no response. I woke up this morning and played with it for a few minutes and found a connection and my MacBook charged throughout the day. However, I took it off tonight, and when I reattached it, it wasn't working. I tried readjusting for 10 minutes but to no avail. I cleaned both the pronged end of the plug as well as female end on the notebook with rubbing alcohol, but that didn't work. What am I doing wrong? Is there a problem with the chord or with the MacBook?