I found the solution; my issue was with the type of Mini-Display to HDMI adapter. It was a passive adapter.
The only important thing is to use the active mini-Display-Port to HDMI adapter as it explained here:
I tried following adapter and it works fine (black one):
You should connect the board to monitor with the adaptor and then power recycle the board, then you should see that the PYNQ will appear! Like this:
