Page Cache (disk basic or enhanced) doesn't work at all

W3TC v. 0.9.2.8 and WordPress 3.5.1
I noticed that my page load is slow, so I checked the timestamp and it changes at every page load = the page is not served from the cache (obviously I checked with a non logged-in browser).
So I have looked for the cache directory and… the /page_enhanced dir is empty!!! Just the htaccess file in it.
I have tried to delete the dir, so W3TC would have recreate it… and it does. It has 755 permission, but also with 777 the problems still there is.

But the plugins says at the end of every page:

Minified using disk: basic
Page Caching using disk: enhanced
Database Caching 41/52 queries in 0.034 seconds using disk: basic
Object Caching 4108/4167 objects using disk: basic

and the “Served From” timestamp change at every page load.

Minify, database and object directory seem to populate normally.

I tried to enable the Page Cache Debug mode, but this way the Page Cache seems to be disabled at all, and the comment at the end of page indeed is:

Minified using disk: basic
Database Caching 36/52 queries in 0.040 seconds using disk: basic
Object Caching 4108/4167 objects using disk: basic

or with logged in user:

Minified using disk: basic (User is logged in)
Database Caching using disk: basic (User is logged in)
Object Caching 4271/4328 objects using disk: basic

and nothing else.
In my wp-config.php the is the define('WP_CACHE', true); line, so it should works fine.

I’m using PHP 5.2 and Apache. Really don’t know what to do. Another cache plugin like WP-Super Cache works without any problem, but I would like to use W3TC.

Help me please.
Thank you

http://wordpress.org/extend/plugins/w3-total-cache/