Can't connect to Internet Explorer, Firefox, Steam, etc.

I can't connect to MSN, AIM,nor can I open the launchers for some MMOs I play (though I can get into them if I launch the .exe file). I can connect to Steam and talk to people but I can't use the browser aspect of it. Firefox says it's a proxy issue, but I'm not too software savvy and don't really know what to do with this. It seems to be anything browser-related. I haven't installed anything new and I ran a few scans for viruses, malware, etc, and did a few other things I usually do to remedy connection issues (disabling firewall, power cycling modem/router, etc) to no avail. Does anyone know how to fix this?
 
What are your computers complete specs? What version of Windows are you running? What kind of Internet service do you have? Cable? DSL?
 
Alienware M18x laptop, 750GB 7200RPM HDD x2, dual NVIDIA GeForce GTX 460M 1 GB, quad-core i7 2820QM @ 2.3GHz, 8 GB 1600MHZ DDR3 RAM, Windows 7 64-bit, Cable. Currently wireless.

It's only an issue with this computer though, as far as I can tell. I have five other computers in the house and they're all able to run these things.
 
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