iMac will not restart after being unplugged...

You are a little low on RAM but nothing too serious. If you are having problems with the Pram battery, as Gary suggests, take it into your local agent. It shouldn't be too expensive, though never having had to do that, I cannot be sure.

I suspect you may need to reset the SMC as per the document below. Read to see how it relates to your problem.

Intel-based Macs: Resetting the System Management Controller (SMC)

If this is outside of your experience, your local agent can do that for you, too, but I think you could do it. Print out the document before you try and make sure everything is backed up.

PRAM battery failure >> black...: Apple Support Communities

Macintosh Family: Batteries and Part Numbers, Part 2 although it's a commonplace CR2032

iMac Intel 20" EMC 2105 and 2118 PRAM Battery Replacement - iFixit

This could have been caused by you unplugging the system when there were applications Open.

What do you mean about (If I Pull and Replace the Plug it will not Restart)

If your computer has restarted normally then If you need to get off the computer Walk Away and it will go to sleep and when you want to restart the computer just wiggle the mouse and left click it and it will come awake and ready to use.

You need to use the Black Apple upper Left and scroll down and use those options.

to shut down.

Good Luck

Don

I understand exactly what you mean ... I think, 😀 One question, though. Do you shut down the machine before you pull out the plug, as opposed to it being in sleep mode or worse still, in operation. You don't actually say so.

If you do shut down, then I would suggest replacing the power strip, or testing with a different one. Be sure to eject any peripherals that are attached properly before you disconnect the power strip.

Time Machine will not be affected unless you fail to reconnect it. When you do it should pick up from where it left off. Otherwise I can't see why your machine is doing this. Components can go wrong for any reason at any time and yours (like mine) is an older machine.

It may not be valid but what is your reading of RAM (in activity monitor).

I also highly recommend you buy an APC Battery Backup.

http://www.apc.com

This is a very good choice rather than a power strip. It protects against power surges, It also protects against lightning storms.

This will be the best $130.00 you ever spent.

Your iMac is going on 8 years old. It is showing signs of a dead pram battery. If you have never replaced the battery now is the time. It's a little tricky to do on the 2006 and later iMac. iFixit has step by step directions if you are handy. Otherwise let the Apple store or an Apple certified repair center do the job.

Don't think I can add any more of use. If you go for a new machine be ready for a shock; the difference is sfaggering. Incidentally, you will not be able to use any PPC apps you currently have; the new system won't accept them. Good luck, and thank you for the stars.

Hi galleyleo,

I have the exact same problem (though with 2011 kit) and tried all the steps you tried.

The only thing that seems to work is leaving it unplugged for hours.

On three previous occasions, leaving it overnight worked; this time it looks like I have to leave it longer.

Did you ever find the root cause of the issue?

Thanks!

Take a look at this:

http://osxdaily.com/2012/04/10/shutdown-sleep-or-leave-mac-turned-on/