Mac Freezes when left IDLE I'm having a trouble with my Mac. It freezes totally when left idle for an hour or so and I can't get it to work by moving my mouse, pressing keys on the keyboard, etc., and I have to force restart the OS. I've checked my console, there are no logs in that except for one called system.log

Here's my System Information dialog.


I'm using nVidia GeForce 210 1GB graphics card but it's showing unknown

What should I do? I'm experiencing it since I've updated to Mountain Lion 10.8.5

The data in the system.log file before my first freeze is

Nov 24 10:31:38 localhost com.apple.launchd[1] (com.apple.aslmanager[929]): Exited with code: 255
Nov 24 10:31:39 localhost mds[43]: (Error) LSOF: File '/Volumes/ExternalHardDisk' (fd=24) left open on device 16777221
Nov 24 10:31:39 localhost fseventsd[52]: unmounting: failed to remove log dir /Volumes/ExternalHardDisk/.fseventsd (Directory not empty)
Nov 24 10:31:39 localhost com.apple.kextd[12]: Error reconsidering volume /Volumes/DATA.


Thanks.
[Perhaps this should be a comment rather than an answer, but I don’t have quite enough reputation points yet to comment. Sigh.]

I wonder whether the log is showing cause or effect here. It looks like you have an external drive attached. Since the problem happens at the one-hour mark, and since there are drive-related errors immediately pre-freeze, perhaps the problem is caused by the external drive responding incorrectly when being put to sleep by the system.

Could you try bringing up the “Energy Saver” System Preference panel and unchecking “Put hard disks to sleep when possible” — does the iMac still freeze?