The HP notebooks with a windows Pre-installation of Windows installed have additional HP software installed including HP power management software. What happens is when the HP notebook goes into sleep/stand-by mode the dock will also go into the sleep/stand-by mode. Unfortunately the HP power management software is not able to send out a command to the Dockingstation to exit the sleep/stand-by mode (programming issue in the HP software). After you power off the dock and power it back on it will work again until the HP notebook goes again into the sleep/stand-by mode again.
This can only be fixed by disabling Sleep/stand-by mode on the HP laptops or by reinstalling a clean version of windows without the HP power management software.
A quick way to get the docking station out of standby sleep mode is to disconnect the Power Adapters and the USB cable to the laptop from the docking station and reconnect it. (This works until another command is sent from the HP laptop to the docking station to go into standby.