Ok let's go through the checklist to get these out of the way.
• You have forwarded the ports from here https://support.steampowered.com/kb_art ... -GLVN-8711
• You have set your ip as the DMZ
• You have connected directly to your modem and not the router
• You have reset both your modem and router
• You have opened your command prompt and typed ipconfig /release
then ipconfig /renew
Have you tried all of these? If you haven't and one of them works, you need to try them all. Take the 10 minutes to try them all out.