[Plugin: W3 Total Cache] Minification and page cache error

Greetings All.
My problem with this great plugin is when i changed my current theme with the new one.i had no style sheet! and i knew it’s about this plugin so i checked the home page of this plugin and it gave me 2 errors which means:

It appears Minify URL rewriting is not working. If using apache, verify that the server configuration allows .htaccess or if using nginx verify all configuration files are included in the configuration.

and

It appears Page Cache URL rewriting is not working. If using apache, verify that the server configuration allows .htaccess or if using nginx verify all configuration files are included in the configuration.

so i checked everything and i found nothing.
nothing was wrong with : permissions , .htaccess(es) and when i’m hitting compatibility in W3 total cache it shows everything works properly but in the real it doesn’t!
i’m using apache for my server but i don’t know how to verify that the server configurations allows .htaccess . and i googled for that and i found a article that said you have to check httpd.conf but i couldn’t find it…
so any way , i have a real problem and i don’t know what to do..
any help will be really appreciated!!!]
P.S. : this problems happened some times in past!and it solved by it self and i don’t know how.

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