It must be an issue with your style. Looking at your site now you have the layout like this:
That's at 1366 x 768 screen resolution. Presumably your screen is much wider than this. You'll need to consult your style author about this or if you did it yourself, look at what you have done to create this layout to determine why it doesn't work at much higher resolutions.
Yes it's a pain but as no-one else knows what changes you have made, it's not going to be easy to identify what the problem is.
Of course if you have a duplicate test site (recommended) and have made clear notes for yourself of all edits you have made (highly recommended) then you can sort out the issues on your test site before making changes on your live site.