Hi,
Did you touch any PHP files under this folder:
/templates/flexible_coolmart/layouts/
I don't know what went wrong and you ended up with this kind of corrupted layout.
the #maininner element is missing the "float" rule, which is created dynamically in case there are modules in sidebars or not.
But the solution is easy. Open this CSS file:
thetreeinatesttube.nl/templates/flexible_coolmart/css/layout.css
and include this CSS rule:
#maininner { float:left;}
Regards,
Support & Development