Could someone please explain to me why my computer is shutting down in sleep-mode. In addition, when it happens, the fan goes into hyperblow, which doesn't make sense because it would not be operating if the system were completely shut down. It acts like it is shut down but won't respond or wake up, etc. I re-loaded my system software per the Mac Store Genius' advice, but that didn't work. Is it possible that my power supply is going?