So apparently joining a Garry's Mod server kills my router

[OverSane]

Uuuuugh, I'm so pissed about this, I've had this problem with wifi AND when plugged into my router
Dunno why, but when seeing the server list everything is fine, I can see icons, everything.
Except when I look at a leaderboard.
Everytime I look at it it's blank, nothing,no names, no scores.
Now THIS is the best part about it, when joining a server, my router seem's to go into some panic mode, basically shutting off internet access, since it recognizes it as some DDoS attack.
Then I can't use the internet for like, 4 minutes, and it indicates that I'm connected.
I have open NAT filtering, but I don't know if I should tick "Default DMZ Server"