With my Preferences settings set so that the monitor will go to sleep after 10 minutes and the computer set to go to sleep after 15 minutes (and the "Put the hard disk to sleep whenever possible" option checked), Time Machine would perform its scheduled backups with no problems at all. Also, I could wake my computer by either moving the mouse or pressing any key on the keyboard. After a restart, now the computer goes to sleep and will only wake up by pressing a key on the keyboard and not when I move the mouse. Worst, Time Machine won't perform any backups until I wake up the computer. What can have possibly triggered this change in behavior after just a restart, when nothing else has been tinkered with? TIA PD - For now, and so Time Machine can perform its backups, I have change the Energy Saver preference setting for the computer to never go to sleep...which I'm not pleased with.