The Issue
On numerous Mac computers, Laptop, Desktop, and Tower alike, the Kensington Wireless Presenters (or "clickers") have been having some issues. Plugging them in for use sometimes prompts the Mac to ask the user to identify the unknown keyboard, something that the clicker is decidedly not. Sometimes that message doesn't pop up and the clicker simply doesn't respond.
On Windows, sometimes the clickers simply do not function.
On a Mac Machine
The Fix
If the keyboard message pops up, leave the USB receiver plugged into the machine and restart the computer. Upon reboot, the clicker should work perfectly.
If the keyboard message does not appear, first make sure that the receiver is plugged into a powered USB port and not into a USB hub. You can test if the receiver is getting power by hitting buttons on the clicker. If the receiver is powered, the green light will blink with each press of the clicker's buttons. If the green light on the receiver does not blink, switch USB ports. If none of the ports appear to be powering the receiver, change the batteries in the clicker. You can check if the batteries need replacing if the built in laser pointer does not work. Make sure the USB receiver isn't plugged into the clicker though, otherwise the laser pointer won't work either way.
On a Windows Machine
Laptops
For many Windows laptops, not all of the USB ports are powered. First, make sure that the USB receiver is getting power. You can test if the receiver is getting power by hitting buttons on the clicker. If the receiver is powered, the green light will blink with each press of the clicker's buttons. If the green light on the receiver does not blink, switch USB ports. If none of the ports appear to be powering the receiver, change the batteries in the clicker. You can check if new batteries are needed by using the built in laser pointer. Make sure the USB receiver isn't plugged into the clicker though, otherwise the laser pointer won't work either way.
If the problem persists, restarting the machine with the USB receiver plugged into a powered port sometimes helps. Otherwise, use Device Manager to correctly identify the receiver.
Desktops/Towers
If the clicker is not working, and is plugged into a powered USB port, check to see if Windows is updating the device drivers. Often this task will be going on, and until it finishes, the clicker will be unusable. If the drivers are up to date, it's plugged into a powered USB port, and it is still not working, restarting the machine with the USB receiver plugged in usually helps. Otherwise check the batteries. You can check if the batteries need replacing if the built in laser pointer does not work. Make sure the USB receiver isn't plugged into the clicker though, otherwise the laser pointer won't work either way.