Internet access problems after installing SP2

I had successfully (I thought) installed SP2 on my XP Home
computer. However, after installing SP2, I can no longer
fully access the Internet. It appears that I can contact
Web addresses but not receive data from them. I can log in
to an SFTP site (using my FTP program) getting so far as
asking for my password but I can't see a listing of the
files on the server.

My internet connection is working --- another computer is
using it as well.

I have turned off the Firewall to see if that was causing
the problem. No difference in symptoms.

I have tried both IE and Firefox --- no difference.

I have tried several Web sites --- no difference.

I have rebooted several times. No difference.

Thanks for any help.