Thanks for your reply Acrosicious. Unfortunately your solution does not work for me. The existence of a USB Input device under Human Interface Devices is dependent upon a USB Input device being present in the USB port. So on first opening, the device manager did not list a USB Input Device under HID. I plugged a USB device in and sure enough the entry for USB Input Device appeared under HID and yes it was the last entry in the list. I disabled the 'Allow computer to turn off this device to save power' and tested your solution. Sadly as I said earlier it did not work for me.
Back to the drawing board:-)