A problem that you may run into with some poorly designed USB hubs is that the devices attached or plugged into the hub will no longer show up or get recognized in Windows after your system has been rebooted. You try powering it off and on, then unplug it, re-plug, reboot, etc...
Windows may even hang during boot while the USB hub is plugged in.
A good example of this behavior is the 49-port USB hub designed for the ASICMiner block erupter. It seems the only way to get this working again is to unplug all the devices, reboot the computer, then plug each one back in one by one. Obviously this is not an acceptable way of doing things.
There is a better way
The first step is to unplug the hub from the computer. There is no need to remove the devices from the hub. Once unplugged, reboot the computer. Then open up a command prompt and type in the following commands:
Windows will open up the device manage window. This is however not your ordinary device manager. To continue, activate the display of hidden devices from the view menu.
Scroll to the bottom and expand the "Universal Serial Bus controllers" tree. Notice how some devices are grayed out. We are especially interested in the ones that say "Generic USB Hub". There should be a few that are grayed out.
Right click on each grayed out instance of "Generic USB Hub" and click "Uninstall".
You'll have to do this one by one since Windows has no way of selecting more than one device at a time. Even more frustrating is that you must scroll back down each time the removal is complete. Uhg... At least it's better than having to unplug and replug in 49 USB Block Erupters each time.
Once done, close the device manager window and plug your USB hub back in. Yep, that's right, you don't even have to reboot. In a few seconds you'll hear that pleasant sound of Windows recognizing and activating each one of your USB devices on your very expensive (or cheap) poorly designed USB hub.