Netflix, Wikipedia not loading on one iMac

I've seen posts with similar issues but never a good solution.

One particular iMac on my home network stopped loading certain web sites last night. Netflix, Facebook, Google, Wikipedia, and OpenDNS either won't connect or will take a long, long time to actually display. Most other websites load fine.

This just started last night, never an issue before. Wireless and over ethernet.

We're using UVerse and have all the machines set to use OpenDNS.

An iMac and Macbook running Lion handle everything fine.

One iMac running 10.6.8 is having the issue. Doesn't matter which browser I use.

We reset the modem, tried different DNS settings, cleared history, cookies, flushed cache, all software is updated including Silverlight and Flash.
Repaired permissions, verified the harddrive, ran CalmAVX, zapped the PRAM.

Any other ideas to try? It's getting to the point I'm thinking of just wiping the hard drive and reinstalling everything...though that's not how I want my weekend to go.

 

Ok, it's working for the moment.
After posting I continued trying various options.
Going into System Preferences>Network>Advanced>TCP/IP and setting the IPv6 option to off seems to have done the trick.

All the other computers have it still on, though they're on Lion and not Snow Leopard.

I'm not sure what this setting would matter after many, many months of it behaving properly.

But it's working now.