web page access

My internet access has crawled to a stop. I have XP
firewall, cable modem firewall, Norton security, spam
inspector. All of these worked together just fine until
two days ago, when suddenly everything slowed to a stop.
Disabling Norton helped for one day. Today it doesn't
make a difference. Disabling Spam Inspector makes no
difference. Please help me figure out what to do that
will not compromise security. Thanks so much.