Instructions
Plug your PS3 controller into your PC via an open USB port. A message will appear telling you "Device driver software installed successfully;" however, the controller is not, in fact, ready to use.
Download the "MotioninJoy" driver from its parent website of the same name (motioninjoy.com) or another provider. Choose either the 64-bit or 32-bit version, whichever is relevant for your needs. Open the zip file and run the ".exe" to install the driver. Click "Install" when you receive the message "Would you like to install this device software?"
Ensure you are connected to the internet before beginning to load the USB driver. Run the program and click "Load" on the "Driver Manager" page.
Quit the program and reopen it. This will allow the driver to detect your controller. Select "Analog Gamepad 2" in the list of modes and click on "Enable." Your controller is now set up for use on your PC.