Cannot Log-In

I am trying to log-in to edit my site, but noticed that there is an error: Fatal error: Call to undefined function wp_cache_get() in /membri/pbpath/wp-includes/option.php on line 1117

Seems like something is wrong with the W3 Cache plug-in. I want to disable it, but I cannot even log-into the website.

Please help.

Hi, this is the Italian support forum, for support in English please write in the international one.
We manually recovered your blog, now you have to remove W3 Total Cache. Use the AlterVista cache instead (you can find it under Settings in the WordPress administration panel), which is much more performant.