Can't create a multiplayer server for me and my friends

When ever I want to make a server for my friends it does and doesn’t work I can create the game as an internet game but when it is started it tells my friends that the server is unresponsive when it is running just fine. And if someone tells me to use Hamachi just don’t hamachi is bad it opens a back door to your computer for hackers. And it’s not a port forwarding problem because my router doesn’t have a firewall active so I don’t have to port forward aka all ports are open to my computer and I have no antivirus and gmod can pass through my firewall. Please help

If I was you I would get an antivirus and a firewall. You are WAY too open for attacks.

it wouldn’t be worth it the computer has no valuable data just steam only program on it and I don’t use the web browser and this does envy help me my OS is Windows 98, XP and on my good PC with antivirus and firewall windows 7