I'd think that this was a DNS issue, but if you can reach the root domain, it's highly unlikely.
DavidR is correct as well, if hosts was configured to load the page on an alternative address, the root domain wouldn't work either.
Maybe there is something wrong with your broadband modem or router.
I've seen weird things like this happen when a modem starts failing, and it loads many different webpages, but not all of them.
It's a longshot, but still a possibility. Have you had any brownouts / power outages / etc recently?
If you can reach the website at home and not the forum, and reach everything at your work, you pretty much nailed it on the head. It doesn't seem like your computer has anything to do with the problem. Next would be your switch / router / or modem.