Whenever I try to shut down my iMac (3.2 GHz Intel Core i3, running 10.7.3), it closes out all programs, goes to the gray screen with the spinning ball and just hangs there. This occurs in restart or shut down mode. Any thoughts?
Zap the PRAM and reset the CMS
A small amount of your computer’s memory, called “parameter random-access memory” or PRAM, stores certain settings in a location that OS X can access quickly. The particular settings that are stored depend on your type of Mac and the types of devices connected to it. The settings include your designated startup disk, display resolution, speaker volume, and other information.
Resetting PRAM may change some system settings and preferences. Use System Preferences to restore your settings.
How to Reset Your Mac's SMC
The method for resetting your Mac's SMC depends on the type of Mac you have. All SMC reset instructions require shutting down your Mac first. If your Mac fails to shut down, try pressing and holding the power button until the Mac shuts down, which usually takes 10 seconds or so.
Mac portables with user-removable batteries (MacBook and most MacBook Pros):
Mac portables with non-user-removable batteries (MacBook Air and some late 2009 MacBook Pro models):
Alternative SMC reset for Mac Pro: If you have a Mac Pro that isn't responding to the normal SMC reset as described above, you can force a manual SMC reset by using the SMC reset button located on the Mac Pro's motherboard.
Try booting into Safe Mode and see if the shutdown issue exist.
You can also open Activity Monitor in the Utilities folder. Select All Processes from the Processes dropdown menu. Click twice on the % CPU column header to display items in descending order. If you find a process using a large amount of CPU time, then select the process and click on the Quit icon in the toolbar. Click on the Force Quit button to kill the process.
Causes could be:
Hope that helps.
If you have any attached external TB, FW or USB devices other than keyboard & mouse, dismount them first, (if mass-storage devices,) then shutdown & see if it completes.
I have a client (my Mom) whose Mac Mini had the same symptoms and found that she'd kept a USB thumb drive physically attached & had forgotten about it. It had been there for some months, but at some point something happened to the drive (out of space? corrupted directory?) and when it was removed for troubleshooting, the Mac shut down normally. She'd gotten into the habit of forcing the power-off, too. Ouch.