2.7.1 and my plugins

any of the plugins that shows on the blog stopped working.
i am referring to those plugins that are used as widgets.
for example, the Let It Snows! stopped snowing while the Akismet is still catching spams.
wp-polls is not letting people vote, but the mailpress still works…

specifically, the following plugins are not working:
1) let it snow,
2) lightbox 2,
3) wp-polls,
4) wp-polls widgets, and
5) twitter tools

it works fine again
after i put this piece of code been in my header: <?php wp_head(); ?>

thanks all