This contains a comprehensive section on USB and your PowerLab. Make sure that your PowerLab is connected properly to your computer and turned on. Check that you have the correct cable and that it isn't faulty. You can try using this cable with another USB device or try another cable with the PowerLab to check this. Make sure that you are using an appropriate version of ADInstruments software.
Earlier versions have USB support.
See above for a list of compatible software. Ideally you should use the latest version of software. The latest versions contain bug fixes and improved support, so may fix problems you experience with earlier versions. For a list of the latest versions, see the current release software for Windows page. USB drivers are installed by the software and are required for your computer to recognize when your PowerLab is connected or disconnected.