Web Server Hosting Net

this last summer i had my computer directly connected to my modem, and i was Hosting listen servers for coop games with my friends without any problem (killing floor and synergy), i got a router a month ago and since then i only played games more suitable for Dedicated servers like team fortress 2 and call of duty, but when i tried to host a gmod server lately it wouldn’t let me, i looked it up and i forwarded all the half life 2 ports (at least i think i did it correctly, i followed a tutorial) but it still didnt work, so i thought every now and then when i want to host i can just connect directly back into my modem. But that doesnt seem to work anymore! this is very frustrating and its getting ridiculous that every avenue has been exhausted as far as i know, and before you say to forward your ports, like i said before that is likely not the problem because it doesnt work straight to the modem either, if there is anything i left out ask me, thank you