iMac will not shutdown or restart!

[Mr Astonishing]

All right after doing a lot of research and trying other suggested answers I am coming to a forum for help.

I recently bought a used iMac in beautiful condition from the classifieds; however, I did a clean install after frustrations with the iMac not properly shutting down or restarting. The problem seemed to be fixed, but after some days it has came back. I can tell you the computer runs beautifully and has no other problems. It's also shuts down and restarts fine after just turning on the computer, but after running a couple hours it will not properly shut down or restart; the dock disappears and it just freezes on my desktop wallpaper. It has no problem sleeping. I also always check to make sure applications are closed/quit before attempting to shut it down. The OS is Snow leopard, and I have tried the following:
1) Repairing the disc
2) Clean Install
3) Resetting PRAM
4) Resetting SMC

The problem is still here and it is very annoying. I can also inform you that I usually have my external hard drive and iPod Touch plugged in.

Hopefully you guys can help me and any suggestions are appreciated.

-Russell

 

[vmachiel]

Try it without those thing plugged in. And if that doesn't work, the only option left, since you tried most things, is to go to and apple store and ask for help. Even though you bought it second hand, maybe they are able to help you

 

[satcomer]

Open /Applications/Utilities/Console and watch the log file to see what program or program error is preventing sleep. A little detective work might help your situation.

 

[Mr Astonishing]

Thanks for the suggestions! It actually looks like unplugging the connected devices fixed the problem. I will update in a couple days to make sure this is the actual fix. Also, if this is the problem how do I solve it? Always unplug my devices before shutting down the computer?

 

[Blakemam]

Were you ever able to figure out how to fix the problem? I have the same problem on an iMac with 2 external hard drives. It has been 6 months since I added the second hard drive and just recently the computer won't shut down as you describe above.

Any help would be much appreciated.