Open the lid and nothing? Tap keys, change brightness, close and re-open lid and your MacBook still in sleep mode?
If you open your MacBook lid and notice that you can’t wake your MacBook from sleep, it’s because of the Safe Sleep system Apple designed. This system puts all your current memory (your RAM) onto the disk, so that it can power down the RAM, save energy, and keep the current working state of your computer, even if you ran out of battery power, changed batteries, etc.
Problem is, it’s slow. And buggy. Often when waking from sleep by opening the lid, the MacBook will remain in sleep.
My solution to this: don’t use Safe Sleep. Unless you’re constantly working on battery power and hate plugging in, you likely won’t ever notice you’re not using Safe Sleep’s hibernate to disk mode.
Here are some instructions on how to turn off Safe Sleep on a MacBook Pro Leopard or Tiger to avoid wake-up problems.
If you still want to use Safe Sleep with disk caching of RAM, use Smart Sleep by Patrick Stein. This software adds a preference pane to your Mac, allowing you to not use disk hibernation until you reach a low battery level, say 20% remaining battery.