sounds like the work of a DDoS attack.... we do have enemies... they probably decided to get some zombie computers to do continual page access attempts, which would mean some would be blocked from access while others would connect and stay connected. As long as you kept a window open and connected to the forum, you would likely keep a channel open for you, while anyone else trying to access the site would get a 404 error.
Actually, these symptoms aren't what I experienced.
There are apparently two routers attached to this web server. In some routing decision, some sessions get to the server via Router 1, and some sessions get to the server via Router 2:
Those going through Router 1 were able to access the site and it was responsive with no sluggishness or errors.
Those going through Router 2 were unable to get the server to respond. I saw half-open (SYN_SENT) sessions on my end indicating the server was not getting my SYNchronize request, or it's reply was unable to get back to me. At no time did I receive a 404 (file not found) error.
I provide these details not to correct you, but rather, to provide additional information that will hopefully be useful to site admins in troubleshooting the issue.