I'm having trouble charging my 2011 15" MBP. I purchased it from Amazon about 2 weeks ago. When I attach the MagSafe adapter to the computer, the computer indicates that it is running on AC power but is not charging. The light on the MagSafe adapter initially turns green, but after a few seconds it simply turns off. My battery has been stuck at 74% for 2 days now. I have cleaned the dust and debris from the computer's AC port and the MagSafe adapter itself. I wasn't having this problem for the first week and a half that I had the machine. Do you think this is an issue with the power adapter or the computer? I am away at college where there are no Apple Stores, so I'm trying to find the easiest way to solve this issue.