Access denied for all (most?) users in all site collections of web app

Hi,

I have a Sharepoint 2010 farm pre-SP1 (yes should be updated!) and for all site collections of a web app, all users are getting access denied.

Now in my title I said "most?" because I have found one user in another office who does not have this issue. This web app/site collections also do not go through f5 or any proxies.

Even if I add myself as a site collection admin via central admin, I get the same result. I've looked at everything, windows time on the server (not using kerberos), errors in event log (nothing), uls logs just say access denied (very helpful!), etc...

I can try what's suggested at http://social.technet.microsoft.com/Forums/en-US/e66f1b09-605d-4546-a581-2a9283c238c0/access-denied-for-all-users-and-for-site-collections-owner?forum=sharepointgeneralprevious but when asking colleagues, there's been no changes, let alone with those accounts? I can do a get on the property tomorrow to find if there is a value set first, however.

Any suggestions on this?