Try connecting your computer directly to your modem and then attempt to connect to the server again.
If you are still unable to connect, reboot your modem and computer by unplugging the power cord from your modem and turning off your computer. After a minute or two, plug the power cord back into your modem and wait for all of the lights on the modem to turn back on. Once all of the lights are back on, turn your computer back on again.
If you are still unable to connect, call your internet service provider and ask to have forwarding ports 5060 UDP, 5061 UDP, 13000 UDP and 13001 UDP opened. After they have confirmed that the ports have been opened, repeat the rebooting instructions above.
If you are able to connect through the modem but not the router, log in to your router and open up the same forwarding ports (if unsure how, please contact technical support for the manufacturer of the router and again proceed with powering everything down and turning back on).
Please remember, anytime powering down your devices, that when you turn them back on, you will want to follow the chain. First, make sure the modem is back on, all lights indicating activity, then the router (if using one) then the computer.