Ok, if multiplayer not working here is quick solution for win 10:

When I click on myltiplayer, and go to public server and select any server to run, my game gets freezed.

Here is my solution, which let me play on multiplayer::::::::::

Goto df2 directory, in my case:
C:\Program Files (x86)\Steam\steamapps\common\Delta Force 2

right click Df2.exe and go to properties.
Go to compatibility tab
click, run game on compatability mode: windows xp (service pack 2)
then click and select reduced color mode: 16 bit (65536 colors)
then click and select run in 640x480 screen resolution
then click and select disable full screen optimization
then click and select run this program as administrator.
then click apply
then click OK

Now open steam and start df2, This will let you play on most of the multiplayer public server(Not all, some might get freez).