There are two generatorions (types) of Garmin ANT USB sticks that need different drivers. Both driviers, however, are available in the "Downloads" section, and both should be supplied by Microsoft's automated driver download as well.
First step of a diagnosis would be: plug in your stick and open the Windows Device Manager to see if the stick has been detected by Windows and if drivers are properly installed.
Another consideration: do you use OTHER ANT enabled software on your PCs, e.g. Garmin ANT Agent.
If yes, ensure that this is NOT running. Otherwise it will grab your stick and won't allow other applications to use it.
If you have similar problems on 3 PCs, there's a good chance that the stick is defective - although this rarely happens.
Cheers,
OMB
