I wrestled with this problem for two days straight and I feel it's
worth passing the information on to others.  I have a SpeedStream DSL
modem, a WRT54G router, and a Windows XP machine.  My modem worked
fine, my router worked fine, but my XP machine couldn't ping any
outside address or renew its IP.  I finally realized that it would
startup with the correct IP, but once Windows was fully loaded my
connectivity stopped.  It was obviously the work of some malicious or
malfunctioning program (the latter in my case).

Don't just check the taskbar and tray, use task manager to look at all
of the processes.  If it's not crucial and it uses the internet then
close it.  This includes your firewall; don't just disable it.
Anything that can't be forcibly closed is probably not working
correctly and should be investigated further.  If you can't kill the
process try disabling it in the startup sequence using "msconfig".  Or
you can try and rename the executable, if you're allowed to.  If all of
that fails (to keep the program from running) you should probably just
uninstall it.

In my case Sygate Personal Firewall (smc.exe) was running and I
couldn't close it or keep it from loading.  I had to unistall it, and
once I did my internet worked like a charm.  Beyond that I don't have a
lot to say.  You'll find tons of other suggestions roaming around the
newsgroups.

Can you disable it first and receive IP?

Bob Lin, MS-MVP, MCSE & CNE
Networking, Internet, Routing, VPN Troubleshooting on http://www.ChicagoTech.net
How to Setup Windows, Network, VPN & Remote Access on http://www.HowToNetworking.com
  I wrestled with this problem for two days straight and I feel it's
  worth passing the information on to others.  I have a SpeedStream DSL
  modem, a WRT54G router, and a Windows XP machine.  My modem worked
  fine, my router worked fine, but my XP machine couldn't ping any
  outside address or renew its IP.  I finally realized that it would
  startup with the correct IP, but once Windows was fully loaded my
  connectivity stopped.  It was obviously the work of some malicious or
  malfunctioning program (the latter in my case).

  Don't just check the taskbar and tray, use task manager to look at all
  of the processes.  If it's not crucial and it uses the internet then
  close it.  This includes your firewall; don't just disable it.
  Anything that can't be forcibly closed is probably not working
  correctly and should be investigated further.  If you can't kill the
  process try disabling it in the startup sequence using "msconfig".  Or
  you can try and rename the executable, if you're allowed to.  If all of
  that fails (to keep the program from running) you should probably just
  uninstall it.

  In my case Sygate Personal Firewall (smc.exe) was running and I
  couldn't close it or keep it from loading.  I had to unistall it, and
  once I did my internet worked like a charm.  Beyond that I don't have a
  lot to say.  You'll find tons of other suggestions roaming around the
  newsgroups.

Robert L [MS-MVP] wrote:
Well, when the problem first started I just disabled my firewall and it
still wouldn't work.  A few other factors may have been involved at the
time so the firewall alone may not have been the problem.  Eventually
though I realized that the firewall was running, basically without my
consent.  I couldn't close it or bring it to the front.  My only option
was to just remove the program.

So I would recommend you try to disable the firewall first, but if that
doesn't work you should consider the possibility that the firewall is
malfunctioning and shouldn't be running at all.  Again, check the
process list and make sure it's not running in the background (it could
be running as a service).

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