Connection failed after four retries?

I have no idea what is wrong with my GMOD, I tried restarting and, I tried restarting my modem. But, Nothing seems to be working. I was playing fine all last night and all day yesterday but, now everything is not working… It’s extremely aggravating, I would love if someone could help me out… I really want to play GMOD D:

Are all the nesicarry ports open on your router?
Also make sure Gmod isnt blocked on your firewall

so are you trying to join a server you are hosting? or is this happening for every server you try to connect to???