No Power to USB ports

I have a U3415W monitor. It was working fine with a remote USB 2 hub. I decided to buy a USB 3 hub and connected it in the same way as the USB 2. That is to say, the feed lead came from an ordinary USB outlet on the monitor (not the high power one).

It did not work and now I have detected that the three USB ports on the underside of the monitor (The high power and the two other ones) are not functioning. The USB on the back of the monitor is functioning fine and is now serving the hub.

Is there a way of re-setting the power to the USB ports?

Thanks

Graham