File header.php corrupt

Hi,
I'm trying to use this amazing theme on my blog but the file header.php seems to be corrupt. Once I installed it this message is shown in the WP dashboard: "Your theme needs to be fixed for plugins to work. To fix your theme, use the Theme Editor to insert <?php wp_head(); ?> just before the </head> line of your theme's header.php file." But there's no </head> tag in the header.php file.
And if I'm am logged in WP as admin, I can see the homepage of my blog despite that message, but if I'm logged out I see only a blank page. I think is just for the reason explained above.
I've tried to fix it by adding <?php wp_head(); ?> and </head> in the header.php but I'm not so skilled in php...so I'm still going crazy!!
How can I fix it?
Thanks :-)

Ok solved!!
It was just an incompatibility with one of the plugins installed in my WP.
The infamous one was the "Acurax Social Media Widget".
I have simply deactivate it and now the theme works fine.
This might be useful for someone else.

Bye!! ;-)