email connects but browser has trouble

I have internet access through a cable modem and a home network in Windows.

What would cause me having intermittent trouble connecting with my browser
while my email and home network have no problems connecting? The problem is
intermittent and I believe is not caused by browser settings because the
browser (either IE6 or Firefox) will connect fine a number of times and then
suddenly no longer connect to the very same websites giving the "Server not
found" error. Why it connects sometimes and cannot find the server at other
times is what I cannot figure out. I do have a firewall (ZoneAlarm free)
but I have not changed its settings.

Looking at the Firewall alert logs - and these listings do NOT correspond to
when I am having trouble - I see that sometimes Zone Alarm will allow a
connection to go through to another PC on my network and other times will
block access to the same PC even though I have its ip is added to my trusted
zone! Maybe the difference has to do with the ports used? The blocked
attempts are from my 1662, 1659, 3436, 3434, 3430, 3425, etc. port to the
other pc's 139 port - if that explains anything. I do not know enough about
how ports work to understand this.

Any advice would be very appreciated.

Jeff

 

Just to clarify, intermittently it may be both email AND browser that cannot
connect. It is the Network (accessing files) that never fails. Sometimes
the email works when the browser cannot connect and sometimes both go out.

Jeff