Joomla 1.6 menus not working

[Sheridan]

I managed to finally upgrade my Joomla 1.5 site to 1.6 and have begun setting everything back up.

 

But the major problem I seem to have already is that no menus or links work properly. For example I have menus on the left hand side which point to single Articles, and hyperlinks on pages that also point to single articles.

 

But when I click them, all I get is a blank white page with the Article title in the top left - all of the articles are there and look ok. Even the sub menus aren't expanding when clicked, you just get the same white screen with the menu title in the top left.

 

Very odd - am I wasting my time trying to repair this or has something gone horribly wrong!