iMac shuts down

At times the iMac just shuts down and then starts up all by itself.
Everything that I was doing reappears back on the screen after I touch the keyboard almost like an interruption and or like going into sleep mode all by itself.
Any suggestions.

Check your settings in System Preferences > Energy Saver to see how long it's set to turn off the monitor etc.

- Simon

Does it come alive really fast when you hit a key? If so, it's in Sleep mode. Do what Buzzard said and check your energy saving preferences. You can see how long it takes to Sleep the computer or turn Sleep off completely if you wish.

Thanks but I should have mentioned that the time is set for about 10 minutes.But I also noticed that there is a check mark in the box for "Put the hard disk to sleep when possible"
Could this be the issue?

All that does is stop the hard drive from spinning to save energy. I still am confused as to what is happening. It sure sounds like Sleep mode to me but maybe it's the way I am understand your wording. How long does it take before it goes dead? And then you hit a key and it comes back up the way it was?

Try disabling Airport and see if that helps. I had the same issue and it was a bad card.

Airport is disabled as for shutting down its instant and once I press any key it comes right back on in the same way it was before shutting down.Does not happen all the time just once and awhile.

macbell10 said:

... as for shutting down its instant and once I press any key it comes right back on in the same way it was before shutting down.Does not happen all the time just once and awhile.

Click to expand...

That is not shutting down. That is going to sleep.

If you want to change the time frame of when it goes to sleep, you'll need to adjust your settings in Energy Saver preferences.

Starting back up "all by itself" is not the same thing as having to "touch a key" to wake it up.
Sounds to me like you have the Display Sleep setting too short for your preference.

So even if there is activity with the iMac the Display Sleep will still go into effect?

Display yes if you have it set to sleep the display in x amount of minutes. You can set it to never sleep the display or sleep the computer if you want.

When the screen goes dark you are not using the mouse or keyboard at the time correct?

Correct-so the issue is as has been stated the time set for Display Sleep.
Thanks to all.

No problem