I am having the weirdest issue on my MacBook Pro. It randomly shutdown while using it. However, it never does so when I have it plugged into an external monitor. There are no shutdown reports or Kernel panics. So far I have reset the SMC and PRAM but no to avail. I also took the Mac into the Genius Bar and they cleaned out the clogged fan, ran various graphics test and overnight exhaustive test for 48 hours but found nothing. I am still having the issue and am forced to now use my macbook pro only with an external monitor to avoid random shutdowns.