It's a power problem.
A usb port can only put out 500mA.
A usb hub uses roughly 100mA.
That leaves 400 mA for the devices.
Run dedicated 5 volts to the hub's power input if it is a powered hub. If not, get a powered hub.
It's usually a good idea to run a dedicated USB cable for the touch screen, that way no matter what happens you can still control the screen.