If LabTutor is failing to detect a connected PowerLab it is likely that the LabTutor Kernel has been set to start in Analysis Mode. To enable scanning for PowerLabs do the following:
1) Open LabAuthor and create a new experiment
2) Go to the LabTutor Kernel and select 'Edit' -> 'Preferences' -> 'PowerLab Startup'
3) Select to look for PowerLabs on USB
4) Close LabAuthor
The next time the LabTutor Kernel launches it should detect any connected USB PowerLabs.