Forum Columns Not Working - Stacked On Top of Each Other

I'm having a problems with my Forums. Please have a look: http://www.greeksyndesi.com/forum/

Notice how the columns are stacked one on top of the other.  I've tried to solve it by making changes in Page Builder, but it's not helped.  I've cleared the cache in the Admin section, and on my browsers. There aren't any recent posts to the forum that might have caused this.  This site has been working fine for a year.  Just started happening.

Any help is greatly appreciated.  Thanks!

I know you stated you have done changes in page builders but try again and clear cache's manually. 

Try builder-->page blocks-->forums home     and make either the left column (forums index) or right column (recent topics) 13px smaller.

Looks like together they are 13px to large. So try making one of them 13px smaller. Then clear cache's via ftp leaving any htaccess files.