We have 2 refurbished MacBooks running Leopard and have the same issue with both of them. When they go to sleep there have been times where they will not start up. Either opened or closed. I hold down the power to restart because it feels like there's nothing else I can do to get out of sleep. This has only happened twice on each of them but it is an issue that seems like it may be my fault. One is a year old and one is a month old.