You need to open a port for incoming traffic. Read the following tutorial on how to open a port:
To open the port TCP 1723 for example
First step is to determine the MAC or Physical address of you network connector. Go to Start --> Run --> cmd --> enter --> a black box will show up and enter the following --> ipconfig /all (notice the space before /all) --> enter --> now look up the Physical address and write it down.
Notice that Physical address = MAC address
Firewall --> Advanced --> Network Security policy --> Global Rules --> Add --> fill in the following:
Description: Incoming Port
Source address: Any
Destination Address: Choose MAC address and fill in the found MAC/Physical address
Source Port: Any
Destination Port: 1723
Then push Apply --> Now make sure that the new rule is somewhere above the basic block rule(s) as the bottom (the block rules have red icons); you can drag and drop the rules --> Ok.