Cannot access certain sites

Hi,

I used to run Windows 2000 Pro on my home PC, with IE6
6.0.2800 (can't remember which service pack) and I could
happily access any webistes I chose to.

I upgraded to Windows XP (SP1) & IE6 (6.0.2800.1106.spxp2
SP1) a few weeks ago and since then I have had problems
accessing a number of different websites. Some of them
are just normal websites and some fail trying to load
applets etc. I could access all of these before the
upgrade.

Also, the pop-up blocker keeps preventing different me
from accessing other sites and the pop-up blocker menu is
missing from the tools menu bar so I can't switch it off.
It is all driving me nuts and is extremely frustrating.

Please can somebody help?

Many thanks,
Kevin