BLue on blue isn't an intuitively attractive color scheme for the "logo" or "title". It's difficult to read and your "logo" is smushed making the words unclear. ergo, you've turned blue, usually associated with calm, into an irritating color.
You use whitespace to frame the actual forum itself drawing the viewer's eyes to the center, shadows on either side contrast out the entirety of the forum to highlight this, but the uniformity of everything within does not allow the user to focus on anything. Size of text for both headings and links are all uniform and there is no easy to lock on point. This layout implies you want the viewer to read everything from top to bottom when, in fact, that's likely the last thing you and a visitor want.
User login is hidden above the banner blindness line. The Archive and Register functions are not intuitive and "Log in to check your private messages" is redundant and confusing to the eye.
And the fact that the overall format is very much consistent with nigh every other forum out there means you have nothing original to catch a viewer's attention and differentiate it from the bagillion other forums out there.
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