-the rest of your internet works fine? (webbrowser, other online gaming,...)?
-have you installed more than one network adapter (LAN, WLAN, UMTS,...)?
-for testing purpose,
SHORTLY disable your firewall to rule it out as cause. do the same with a possible antivirus software. enable again after testing!
-are you able to list hardware between your pc and the internet? (your router,... etc). are you maintaining these devices? if not, who is?
this is all standard procedure, shotgunned into the dorkness.
hard to tell from here. maybe a real dev (who also has insight into lobby network mechanics) looks into your issue, im only with the police (admin).