I have been doing Tech Support for several years now and I can usually solve most OS or Internet related problems, but there is 1 problem I have found no solution for as yet.
When a PC can connect to the ISP through a Dial-UP modem and stay connected, but is unable to browse.
Also MSN...ICQ and any messaging program is also unable to connect.
In a command prompt IPConfig tells me the computer has received an IP address
and is not generating one randomly, but pinging either domain names like www.google.com or pinging IP addresses comes back with no reply.
Pinging 127.0.0.1 tells me that TCP/IP is not at fault.
Changing modem drivers,recreating the dialup account in inetwiz with a new name, removing and re-installing TCP/IP and/or updating Internet explorer does not help in any way.
I have noticed this problem in ALL flavours of windows and I am usually forced to fix it with a clean install for the sake of saving time and my sanity.
In windows XP a rollback or a system restore also is unable to help, and as usual the client is unable to tell me what has happened or changed on the PC to cause this problem to begin with. (If I knew what causes it I might be able to find a solution)
This problem is by no means common......it is actually quite rare...but I still am not capable of fixing it without a clean install of Win9X or a SFC /scannow which is basically the same thing in XP.
I hope this message is not too long, but I tried to include all I could remember from my past experiences.
EDIT: It also does not appear to be Virus or Spyware related because all my clients follow my advice and update their virus scanners and have ad-aware / spybot / spyware removers installed, averaging 10 or 20 cookies and spyware every week or so.