A correctly connected and recognised PowerLab should show as an 'ADInstruments PowerLab' within the computer's Device Manager. On some Operating Systems, such as Windows 7, the PowerLab may have a '?' or '!' icon next to it in the Device Manager - if the PowerLab shows as an 'ADInstruments PowerLab' it has been correctly identified, and any Windows warning iconography can be ignored.
An incorrectly recognised PowerLab would show as an 'Unknown Device' within the Device Manager (or it simply wouldn't show up as a device at all).