Today's mystery actually began a few weeks ago, when I updated my Mac Pro from Snow Leopard to Lion (). I had previously upgraded the other two Macs in our house without incident. So I was expecting similar smooth sailing. And, at first, my expectations were met. Lion installed successfully and everything was working perfectly.

It took a few hours before trouble arrived. My Mac began slowing down. I mean slowing down. At first, it was just a slight lag. But, soon thereafter, everything slowed down to the point where if I clicked to drop down a menu, the menu would not appear for several minutes, if ever. Actions such as opening or closing an application were completely out of the question. I could still move the mouse pointer at a normal pace. It's just that I couldn't get it to do anything.

I did my usual first attempt at a fix: I restarted the Mac. I had to use the physical power button on the front of the machine, as no mouse click or keyboard command would work by this point. Happily, all returned to normal--but only for awhile. Within a few hours, the "slowdown extreme edition" once again reared its head.

Donning my Sherlock Holmes cap and a pipe, I set out to uncover the villain.

I restarted the Mac once again. This time, before the Mac started reacting as if it were caught in a vat of congealing taffy, I launched Activity Monitor (an application in OS X's Utilities folder). I monitored my activity. At first, nothing. Then, it happened. The WindowServer process started moving to the top of the "% CPU" column: 25 percent, 40 percent, 62 percent, 78 percent. When it got to about 75 percent, the slow down really kicked in. By the time it topped out at 99 percent (and stayed there), everything had ground to a halt.