Well, after having spent 4 hours/day for 5 days trying to find a solution to this stupid problem, here is what happened:
1) I executed "ping PIDGEON-DSK" on NB.
2) I noticed that IP of DSK was 192.168.56.1.
I thought, strange, DSK was set to a static ip, or 192.168.0.2...
3) I executed "ipconfig" on NB.
I noticed that the network card "Scheda Ethernet VirtualBox Host-Only Network" was associated to the same ip of DSK (192.168.56.1).
4) I remembered that I installed VirtualBox even on DSK.
5) I noticed that the network card "Scheda Ethernet VirtualBox Host-Only Network" had the same static ip on both DSK and NB (192.168.56.1).
6) I changed the "Scheda Ethernet VirtualBox Host-Only Network" static ip of DSK to 192.168.57.1.
7) I tried to access DSK shared folders from NB.
8) No authentication window appeared.
9) I was able to browser/modify DSK share folders.
10) I waited 10 more minutes.
11) No authentication window appeared.
12) I was able to browser/modify DSK share folders.
Problem solved.
In short, this happened because some months ago I installed VirtualBox on both DSK and NB. When you install VirtualBox, it creates a network card so that you are able to connect to internet when using the guest system. The problem is that the network card has the same ip (192.168.56.1) for every VirtualBox installation, so if you connect 2 PC with VirtualBox installed, there will be network card conflicts unless you change the static IP of one of the cards.