Mail receive works but not www or MSN

Hello,

After some virus problems, and update to Windows XP and IE7, I have had the following situation on this computer:

Outlook mail receive works
IPCONFIG and ping an external site works

I cannot send email, browse the internet (either with IE or Firefox), and I cannot log on MSN either. Software auto-update does not work either.

Troubleshooting done:
- called my internet provider - they could not help
- reset all IE settings
- disable Windows firewall
- open ports 80 in the Exceptions tab
- tried to disable AVAST anti-virus, but I only managed to damage it...

Our family are using another computer but now I would like to re-enable that one.

Is there any software tool that I could run from a USB key, to check the Windows settings?

many thanks,
Dominique