Cannot Access Windows Update & some other sites

I am using Windows XP Professional SP2 with IE6. Using 2 pcs ... a desktop &
a laptop with same cable connection. With the desktop i cannot access windows
update & some other sites while the laptop works fine! So the problem is not
with the ISP.

I searched the community thoroughly, tried almost all options ... but no
result yet. IE in both pcs is configured similarly, so there is no problem
with IE configuration as well.

I couldn't even open this page (Microsoft Community) until i used https
instead of http. I also tried windows update with https. At first it seems to
work then it says:

"We've made improvements to our website. To download the new version of the
software and begin using Windows Update, please click Install Now."

When i press install, after 19% installation i get the error msg 0x80072EFF.
Tried to resolve the error as well but the solution is applicable for SP1
while i am already running SP2.

I have also tried registering some dll files mentioned somewhere in this
community … edited some registry values … tried using another profile with
admin privilege … no results yet.

Someone pls help me out!