If you found this problem after approx 07
30 04 june - you may have received the Bugbear 'B' virus.
This virus caused my machine to try & access a non ms site when xpupdate accessed.
Also various other files corruptted & all antivirus & firewall s disabled & unable to be accessed.
Sorry for being a bit pessimistic but required hdisc to be reformatted.
I tried reinstall & as you found didn't work & made things worse.
hope u havn't got the virus - but thought i better point it out.