Network Problem (Can't access game servers on Steam!)

Hi. I had this problem ever since I bought this piece of shit router.
It's a "NetworkEverywhere Model: NWR04B" It's not that bad actually. It
shares the connection pretty good as well as everything else except 1
thing. I can't access game servers with it. Servers on Steam won't show
up, I can't create games because people won't be able to join. I tried
configuring it by enabling DMZ and opening port 27960 and also the
ports that are required for Steam but nothing. The servers still won't
show up. I'm seriously about to throw this shit in the garbage. I can
only play when I disconnect the router and plug the internet directly
to my computer but the thing is that I share the connection with my
sister and whenever she's home I can't play anything and I'm sick of
it. Does anyone have an idea of what it could be? I would be really
grateful.

Also,

- My ZoneAlarm is configured to let Steam fully access the internet.
(And even when it's deactivated it doesn't work much more.)

- Windows firewall is totaly deactivated.

- I even installed NetBios and TCP/IP

- I also noticed that when I try to refresh the server list on Steam,
not just the servers won't show up but it literaly blocks the
connection. What I mean is while I'm trying to refresh the servers list
I can't open a web page it's just searching for it as if it would be
detecting proxy settings and then when I stop refreshing the servers I
can open web pages again. Weird!