This PC has just been connected to this ADSL Network, and for some odd reasons the internet is fully working as it should be. Just Avast has problems downloading updates as it cannot connect to the Avast download server. Nor am I able to play Maple Story on this (my girlfriends) computer. Like above, it is unable to connect to the server.
Honestly, I tried everything and I can't figured out what exactly is wrong. I've released / flushed my dns & renewed my IP address. This PC doesn't has any firewall so that is not the problem. I even attempted to disable the windows firewall. Further more, I even checked in the modem / router settings, and I couldn't really find much at all.. At least, no port forwarding regarding the computer which is a room next to me.. Which fully works with downloading upgrades and can play maple story just fine.
Nevermind, found the problem. My bro has set a proxy on IE (Internet Explorer).