iMac not sleeping and screensavers not activating

[ryan.stewie]

All of a sudden my iMac has just started not sleeping after the time its supposed to and the screensaver wont turn on when its supposed to. I havent installed any new software, its just happened out of the blue, I can still use hot corners to activate sleep and the screensaver but id rather have them activate by themselves. But they're not, and all of my System Preference's sleep and screensaver options are fine. Why wont my Mac sleep and/or turn on the screensaver after set times?

 

[RonelEllis]

re: iMac not sleeping and screensavers not activating

Ryan, thank you for posting this one. This is exactly what is happening with my iMac. Do you think it could be caused by an recent operating system software update perhaps?

 

[Hellhammer]

Have you tried rebooting? That solved my problem. Sometimes it just doesn't want to sleep

 

[RonelEllis]

Rebooting does not change anything.

 

[adammelancon]

Same here, reboot fixes it, but only for a little while, then the screensaver/screen-sleeping won't kick in.

If i kick in the screensaver with the hot corner it will work, but I have screen sleeping set for another corner, when I activate it, it sleeps the display only for about 4 seconds, then it pops back to the desktop.

24" April 2008 2.8Ghz iMac 4GB RAM running 10.5.7

List of apps I use daily:
Firefox
iTunes
Skype (stays connected)
Drobo Dashboard (stays running)

I've heard sometimes your sharing preferences can cause this...
Sharing boxes I have checked in System Preferences:
Screen/File/Printer sharing enabled
remote login enabled

 

[allan.nyholm]

Firefox is known for not letting your Mac sleep. I have the same problem when using Firefox3.5b4(which is my browser of choice these days) - I saw a glimpse of improvement while using nightly builds of Firefox but I'm not sure if it was pure luck or that they have actually improved Firefox in this regard.

My screensaver kicks in fine but the system won't sleep correctly on time out set in System Preferences.

Resetting the SMC & PRAM does not help either. It is simply Firefox if you are using this browser. Or it's some sharing activity keeping the system alive.

 

[si77hay]

I agree with the above post that FF3 is the culprit. Take a look at this thread, in particular post #4.

Not a solution, but PleaseSleep is a work-around that I use.

 

[allan.nyholm]

^^One thing I noticed last night that didn't occur to me before was to close all Firefox 3 windows; leaving neither browser or minimized windows open- and then the system slept. This is the easiest solution. It's often luck however if my system sleeps correctly.

Edit... while it seems stupid to leave Firefox 3 open instead of quitting it - that's just what I did

 

[Jackintosh]

This also came up in a thread a few months ago. The conclusion was that if anything is running in the background, it could prevent sleep. Backup, maintenance, video transfer, and the like.