The touchscreen is not connected or is malfunctioning.
Resolution
Solution 1
Press the Home button. The task you are performing may not be responding, but the franking machine may still be working.
Solution 2
Remove then replace the USB cable between the franking machine and the display.
Please be aware if the touchscreen is still not functioning, you can connect a USB mouse to the franking machine and use that until the touchscreen can be replaced.