Hey buddy!
Are you using Zone Alarm by any chance? Same thing happened to me, turnes out Zone Alarm blocked DC's access to the web. All I had to do was allow access and problem was solved. Also, if you're using incremental patch that may be a problem as well. It was mentioned here b4, people were havong all sorts of problems with the incremental patch, but once they downloaded the full patch, it took care of most issues.