Do you need Microsoft File sharing like \\servername\path to work and it just won’t?
Try this from command prompt:
telnet servername (port)
Example: telnet servername 137
If a black screen appears then the port is open (this is for TCP)
If you get an error then ask your firewall team to allow connections from your external IP to the ip of servername on the following TCP and UDP ports:
TCP: 137,139,445 UDP: 137,138