Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Energy Saving in OSX
Leopard comes with a number of energy saving options built into the operating system. This tutorial will show you how to customise these options and even set your Mac to startup in the morning as you get up and automatically shut down when you go to bed.
The energy saving options are in the System Preferences (click the Apple (?) on the top left of your screen).
The main window allows you to control the time at which the computer and the screen go to sleep. It is important that the screen sleep time is greater than the time limit on the visual screen saver. Leopard will warn you if this is the case and will allow you to adjust it appropriately. I have my screen saver set to load after 5 mins, screen sleep after ten and then the entire Mac goes to sleep after 15 minutes.
Even sleep mode uses up energy and Leopard offers the ability to shutdown and startup the computer at set times. This means you can have your computer turning on at 7am ready to check your email, RSS and twitter and then shutdown at 11pm that night when you are asleep.
To set these times click ‘Schedule’ at the bottom of the Energy Saving window.
Set both times and hit OK. Remember the computer still needs to be plugged in to the wall with the wall switch on to work. With a bit of tweaking you can easily have your Mac working with you in a much environmentally friendly fashion.
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