Question : Can't reach <a rel="nofollow" href="http://localhost" target="_blank">http://localhost</a>

I'm using the ASP .NET Web Matrix Server for testing a page. But when I do and try to access http://localhost:8080 (technically, where the page should be displayed), my Browser gets stuck at "Connecting to localhost..." with 100% CPU use, and nothing happens.
The problem only arises when I'm online (ADSL requiring User and Password), and when I'm offline, it simply works flawlessly. As far as I know (or google told me), it's an IIS problem.
The computer is an Athlon 64 939 3000+ @ 2600mhz - 2*512 Corsair XMS - DFI nF4 Ultra-D, running Windows XP SP2 with every optional program installed (I mean, the ones that come with Windows), I'm using Sygate Personal Firewall and NOD32 (Antivirus). Also, I have Visual Studio 2005 Enterprise installed (Full instalation).
I have to add that this doesn't simply happens with Web Matrix, but also when trying to deploy a Dedicated Server for a game.

What I've been trying is:
* Check the HOSTS file for localhost. It's there.
* Deactivate both the Firewall and the Antivirus. Nothing changes.
* Reinstalling IIS. Nothing changes (I did this: Uninstall from Add/Remove Programs, Reset, Install, Reset, Try).
* Trying with 2 browsers (IE6 and Firefox 1.5). It's the same.
* There aren't any programs using ports 8080 or 80. I checked with netstat and Sygate.
* Changing the server ports (I'm using WebMatrix's Server). Nothing happens.
* Using http://127.0.0.1:8080 . Might sound strange, but it works.

Answer : Can't reach <a rel="nofollow" href="http://localhost" target="_blank">http://localhost</a>

OK - why are you using port 8080?
why not port 80? -Thats no big deal - I was just wondering
I think some of your problem too is the way the ADSL modem is assigning you an IP address - if you are having to use a username or password
Is this a USB DSL modem?? - IF so, you'll want to get an Ethernet DSL modem/ router or even better, I prefer a plain old ethernet dsl modem
and then get a netgear router (they are cheap - about $50) - that USB implementation really bites for use with website development
With an ethernet dsl modem and a router - the router will do your logging on and maintain the line and considerably simplify your
IP address scheme - with this USB thing, you are using a sort of modified network interface card(NIC) that changes its state based on whether you are logged on or not
so when you logon, the NIC (your connection to the internet) assumes an external or public IP address, and therefore the localhost address (which is IP address 127.0.0.1) will no longer work because it is only for "loopback" purposes - it wont "route" like other IP addresses would

Bottom line - if its USB, see about replacing it - if not, then get a router and hook the dsl modem to it
then you can follow these directions for setting up your webserver on the LAN
http://www.experts-exchange.com/Web/Web_Servers/IIS/Q_21667122.html