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I registered on your site, and I see the same behavior you describe. I have created a new topic and I can't see it either.
You don't get a blank screen per say, but a fully populated page, that simply doesn't have the post in it. All of the blocks and headers are there, but no post.
Since you have no data to lose, I would start by updating the forum module in place, and if that doesn't work, I would uninstall the module, and re-install.
You could also use the MySQL debug to see if maybe a query is misfiring, but that's a stretch...
Good Luck,
Rich