Ask Max: Mac Sleep Issues
My Mac does not go to sleep according to whatever time lapse I might choose in System preferences/Energy Saver. The monitor goes to sleep but not the CPU.
Your system can be kept awake when an application is actively working or crashed, regardless of Energy Saver settings. Older applications in particular have problems sleeping, and this cannot be fixed with ™one little pill.™ A good test would be to quit all running applications and see if the computer sleeps properly. If it does, then you just need to open application one at a time and put the computer to sleep in order to find the offending application.
If the computer still fails to sleep after you quit all running applications, then you will have to do further investigation. The best tool for this is Activity Monitor, which can be found on OS X Mac computers in the Utilities folder. In Activity Monitor, use the ™Show™ popup menu to display Active Process. After quitting all open applications, make note of all the non-Apple processes running. One of those processes could be at the heart of the problem. You can then force-quit suspect applications in Activity Monitor, and see if that allows your system to sleep again.