port 80 is closed, plz help

I am having very strange problem. On one of my machines (A)
I have w2k server, using IIS. I have a website there for over a year.

It stopped working yesterday.I noticed that port 80 is closed. I did not make any changes so I thought my ISP (DSL) closed it. I called my ISP and they told me that they did not block any port.
More Over I hooked up my DSL to other computer(B) and port 80 was open.

I thought may be it is the router, i connected straight DSL to computer , but still port 80 is closed

So I thought probably some virus on my machine. But I also have another ISP (cable modem) when I connected cable modem to the same computer (A) port 80 was OPEN. That mean Computer is fine too. I don't know what is going on.

It basically the combination of DSL and computer (A), when problem occurs.....

Your help will be great apprecaietd...

Thanks

if u have a firewall on u might want to check mark that the port 80 is a fine thing to have open and for the DSL u might want to make sure in the settings that port 80 is open and that u are in a DMZ host or some thing like that.

I have disabled the fire wall. Router setting are fine in DMZ too.

I do found out now one thing, If I take router out I
get port 80 open.
But I hooked up same router with other computer and it works fine and give me port 80 open.

I used one another router which is working fine with other computer but when hooked to my this machine gives me port 80 "Stealth"..

Look like for some reason this particular machime is having problem with the routers, no matter what router i use....

The port forwarding setting in the router probably points to the wrong LAN IP address.

well my easiest way would just to reinstall ur OS Windows and see if that helps but if u don't want to do that then just wait for more help with ur problem

There is no reason to consider reinstalling windows.

u naver know, but as i said that would be my easiest way of fixing it.
have u tryed taking thaking the HD out of the computer thats won't let u use port 80 and puting it in the computer that does let u user port 80?

reinstaling OS will be my last resort. It may not make much difference since I also have XP pro on the same machine with IIS. There too I am geting port 80 "stealth" when connected through the router.

I have not tried the hard drive in the other computer.

router setting are correct.......

I wonder if it is some hardware related problem, since I am geting problem both in XP and w2k server

From your description of the problem you're having, it's almost certainly a problem outside of the IIS computer. So my bet is still on a misconfigured router