Why does my Macbook Pro try to shut down when I leave it unattended?

When I close the lid of my Macbook Pro (Lion), it goes to sleep, which is good: it powers down without closing my applications.

But if I just leave the computer unattended for a while without closing the lid, it attempts to shut down instead. It usually fails at this, because there's often a program such as Photoshop (which doesn't use Lion's autosave feature) blocking shutdown with a "Save as" dialog. But it does always succeed, annoyingly, in closing my browser etc. It does this even when the computer is plugged in and fully charged.

When I leave my computer unattended for 15 minutes, I want it to behave exactly as if I had closed the lid: it should go to sleep, not shut down.

How can I do this?

Solution 1:

Try going to System Preferences and choosing Security & Privacy. When that application window opens, choose "General" tab and then look to the lower right corner and click on "Advanced". Uncheck "Log out after _ _ minutes of inactivity.

Not sure but this might be the cause.

Good luck

Solution 2:

Yes, indeed, the "Log out after 60 min" had a check mark. That was the problem. I was just lucky that the OS was unable to Quit certain applications that do not use the built-in Autosave feature, but many times I found myself at the Login screen when coming back to the puter.