I run a 6 year old iMac, with the latest OS In the past few week the spinning color thing has ofter keep spinning when I click on anything. A few times the spinning stopped and all seemed frozen. I did a shut down by the button on the back and then rebooted. All worked well, but later the spinning ball continue to take a long time to activate what ever it was I clicked on. Ideas as to what might be happening and/or how to fix?