Q: mountain lion does not go to sleep

Do some basics. First is Repair Disk Permissions in Disk Utility (Applications - Utilities - Disk Utilties). After that then test and if the problem persists then restart in Safe Mode. You do that by holding down the Shift Key when you hear the Startup Tone until you see a progress bar appear. Once it has successfuly restarted then restart normally. A Safe Mode restart will clear some caches, it's possible one or more is corrupt. If the problem persists, post back.

Got it, OK I think you need to do a couple of basic resets. From the way you are describing things I thing doing a SMC reset will handle it, but you should do both of these resets 2x to be sure.

iMac SMC and PRAM reset

Your welcome.

Thanks!

After doing a mountain lion upgrade, sleep didn't work correctly - In sleep mode, the screen would blank out but the MAC didn't really go to sleep.

Did the steps 2x and it works fine.

Had same problem/issue iMac would not stay a sleep.  Did above resets, 1st SMC 2x and then 2nd Pram 2x also. It appears to have worked... just tested it...Yea!!   Thank you!

The reset did not work...unless there is a specfic sequence to it.  I did the SMC 2x and then PRAM 2x.  iMac still woke up after a few mintues for no reason.  Then I performed a reset on one more time.  Any other recommendations, would be appreciated.

Thanks

Please create your own thread instead of trying to Threadjack this one. Also at the very least complete a profile, we don't even know what iMac you own, version of OS X or anything else. If you do these two things someone is probably going to assist you. If you don't know how to creat a profile please click Profile Update