Hi - how are you? Thank you for your fast reply here. Resetting the SMU did nothing. I will try resetting the PRAM now. Here is the other information about this case, whic I forgot to write yesterday:
(1) When my iMac goes to sleep, and then shuts off automatically, merely pressing the power button does NOT turn it back on, and I must pull out the power cord from the wall, and then plug it back in, in order fo the power button to then turn it back on.
(2) There is sometimes a horrible, scary, loud constant noise when machine is "sleeping", and this same noise occurs when I play some games online. Otherwise, thre is no noise.
Does this no change the diagnosis, doctor? I have backed up all my work, just to be safe. Do you think my hard drive is going south?
Thank you very much for a quick reply, if possible!!
One other thing you should check is to make sure the iMac has a good power connection. If you are currently connecting it to an old or over-crowded "power strip," as a test, try connecting it to a direct wall connection by itself.
What you said with (1) sounds like it could be a power supply issue. By unplugging it, you are doing something like the SMU reset, and that "resets" the power supply so it works again, until the next time it has a problem.
I don't know what is causing (2). Is this sound coming from the speakers, or something mechanical inside the iMac?
And, it may be a dead or weak PRAM battery. If you disconnect it from power, plug it back in, and start it up without an Internet connection, is the time and date set to some odd date/time?
If the main problem is related to sleeping, you may want to just set Energy Saver to do Display sleep, but NOT Computer sleep. That's actually how I use my iMac all the time. When you know you are not going to be using the iMac for a few days, shut it down (power off). If it works reliably that way (when you are using it), keep using it that way until you get a new Mac (or it fails in a more serious way). In the mean time, you should have a good data backup plan in place (like using Time Machine if your OS is Leopard).