Had the same issue. Did all of the above. Turned off firewall and antivirus, set Internet ver(9) to lowest setting on slider, disabled my router use of OpenDNS as well as the dsl modems use of OpenDNS, and rebooted the modem and router, cleared the cache of itunes. went to command prompt and used command ipconfig /flushdns. No success. On every attempt I deleted the iTunes download directory. It wasn't until I unchecked "Always check for available downloads" and then re-applied the check did it work. Maybe it is coincidence??