Problem connecting to friend's server

This is very weird whenever I go on Gmod i cant contact master server NO MATTER WAT! and if i go on CS:S then it lets me be on servers. If I joina friends game… Unable to join after 4 retries. Favs? Nothing. History? Nothing. HELP PLEASEE!

  1. Did you buy GMod?
  2. Have you unblocked hl2.exe in your firewall?