A common troubleshooting technique is to reset your PRAM. This will occasionally clear up problems with your Mac. Learn about PRAM, what it is and how to reset it. Also learn about SMC.
Check out MacMost Now 616: Resetting PRAM at YouTube for closed captioning and more options.
Here’s the link to the Apple page explaining how to reset the SMC: Resetting the System Management Controller (SMC)
I have a Wireless Keyboard and after some trial and error, this pretty much works, if you get the timing right !
After a Full Shut Down...Power on the iMac... then wait for the Chime but Press the 4 Keys that Gary stated before the chime goes off.
So hear chime, then after a second press keys (before chime goes off)
If you do this correctly, it works fine. So do try it.
Apple tech rep told me to let it cycle through 7 times before releasing 4 keys.
OK, where is the link you said you're posting on resetting the PRAM and SMC? Unless I'm missing the obvious, it's not on this page. Please let me know. Thanks.