This issue seems to be reproducable on a number of Snow Leopard 2010 MacBook Pro's - the mac is incapable of going to sleep due to timeout. It goes to sleep fine from keypress or by closing the lid, but when you leave lid open and let it timeout to sleep as per settings, the screen turns off, but the laptop will not go to sleep. How to reproduce: Plug in MacBook into power, unplug all else. Turn off Bluetooth and Airport In Energy Saver settings: Turn Computer Sleep to 1 min on both tabs Check Put Hard Disk to sleep when possible Uncheck Wake for Computer Access Wait. The computer will turn off the display, but the sleep light will remain solid - indicating that the rest of the machine is still running. Is this a known bug? I seem to be able to find many people asking same question and get no answers. Is there a solution or a workaround?