I have an iMac running Snow Leopard. Everything is running fine, but the mac won’t go to sleep if inactive. The settings are correct. Any ideas what might cause this? I guess some background program is preventing the mac from automatically going to sleep, but I have no idea which it is. How can I find out? Is there some logging for sleep I can turn on?
The following Apple Support article can be used as a checklist to diagnose sleep problems:
Mac OS X: Why your Mac might not sleep or stay in sleep mode.
I suggest verifying all the points mentioned in this article, and especially in the section "How can I determine what is causing a sleep issue and how can I resolve it?".