am getting blocked web sites?

[Clark]

I am getting blocked sites whenever I try to go on craigslist auto sales, the message I am getting is that "Internet Explorer cannot open the internet site, operation aborted"....I am running windows XP
what can I do, somebody help, I buy and sell autos and this is blocking me, I have gone into contend advisor but everthing is open......................

[lanshark]

first thing I would do in any case od unexpected computer behavior is run a malware check.
download malwarebytes antimalware its free and in my opinion the best.
http://www.malwarebytes.org/products/malwarebytes_free/

next delete all your history, and cache files from your browser.
if you don't know how google it.

if it still doesn't work reboot your internet modem and router. my router goes funky from time to time and blocks random pages that I go to allot.

good luck