OK, I just wanted to make sure it wasn't an issue in Google Chrome, as I am not using that so really can't speak of there being any issues with that.
But I have been using IE8 for quite a while, and I suspect a good chunk of our users are also. So I would lean toward it being something with your system. Have you made any changes to it recently (installing new software, especially things that want to add their own toolbar), or if this is at work, has your company changed any security settings.
One last idea I didn't mention before was you might want to check our Security settings such as Firewalls, Pop-Up Blockers, etc and make sure nothing is blocking the Message Board.
That's about all I got! I hope you get it figured out.