Are you trying to host via ENT? If so, maybe try other hosting locations. Some tend to not go through prior to various bots within the location. I'd try hosting 2-3 times, if it doesn't work, check the game list to see if other public games are up and running and if so, just try another location.
Also assistance such as this can be provided by the technical support section of our forum and the ENT chat, as RadiantCrystal said.