Just this morning I had a strange problem on my Retina MacBook (13-inch, 2012 model) that I've never had happen before. All of a sudden, a minute or so after starting up the computer, the fans started revving at full speed and I could hardly move the arrow around. I went into the Activity Monitor and at one point it showed "kernel task" at 607% CPU usage. After a while it stopped (no programs open at the time) but then it started up again randomly. What is going on? (I was even able to restart the computer during this "overload", but it persisted through the restart. The only thing that stopped it was shutting it down, but then when I started up the laptop again, it happened again). This really sucks because I was planning on selling this computer (obviously can't now) and I haven't backed up my stuff in a while and I was planning on doing that before selling (and I don't think that's going to be possible now unless I fix this). Any help is appreciated.