Hi pw123,
Can you first go to this site, it will tell you if you're using opendns.
http://www.opendns.com/welcome/If this says you are using opendns then please sign in to your opendns account and click on "network" under "settings" then "add manage networks".
At the very top of this page it will say "your current IP is a.b.c.e"
Is that IP the same as the IP shown further down the page under "your networks"?
Note:
You PC has a dns cache, if the blocked site is in there you need to wait for the entry to expire before the site becomes blocked. Similarly with the browser cache.
Alternatively you can flush the pc's dns cache and browser cache, or just turn the pc off and back on.