Define that for us.
Did not allow USB devices to connect to it?
Did not pass USB 3 on to devices connected to it?
Did not turn on at all?
Question: Do you have USB 3 on your iMac? If not, then you having a USB3 hub will not help you at all.
A little more detail please
Some months ago, I had purchased a Siig USB 3 hub for my iMac. However, I had to return it as it did not work. Has anyone had better experiences with other devices?