I have a mac book pro which is late 2011 version. I am having an issue with it. I have been trying to turn it on; however, I am able to hear the sound of fan working but the screen is not turning on. Plug in the power cord and wait for few moment, the screen is on a little bit, then it automatically off and the fan stops working too. I am thinking about the CMOS battery is bad but i am not sure. Any one had this issue before?