iMac sleep issues - sleeping before it's supposed to
Hi,
As the title says, my early 2008 iMac is having sleep issues. Specifically, when I put the display to sleep (via a Hot Corner or via Control+Shift+Eject) I have recently noticed that my imac goes to sleep anywhere between 2 minutes and 5 minutes AFTER display went to sleep but BEFORE its set time of 10 minutes in System Preferences>Energy Saver. Both the "Computer sleep" and "Display sleep" sliders are set at 10 minutes by default. I experimented extending the sliders out to 20, 30 and 60 minutes and replicated teh same results ie. computer going to sleep 2-5 minutes after I put the display to sleep. The "Put hard disk to sleep", "Allow power button to put the computer to sleep" and "Start up automatically after a power faliure" boxes are normally checked and I tested to see if unchecking these boxes makes any difference but found that it had not.
This problem is really annoying me because everytime I leave the computer for a short break and come back 1, 2, 5 or so minutes later I discover the computer fast asleep. It's even more annoying when I set a program or a CPU-heavy task to run late at night, turn the display off to save power and wake up the next day to discover that about 5 minutes' worth of work had been completed before the computer went to sleep HOURS ago.
So my question is this: why is the computer going to sleep so early when I set it to go to sleep much later?
Your comments and suggestions are welcome and any response would be most greatly appreciated.
My sincere thanks in advance.
Cheers. 🙂
iMac (24-inch Early 2008), OS X Mountain Lion (10.8.3)