Can’t embed video

Hi I’m running a lot of WordPress instances on three different servers hosted and managed by me.
I never had a problem in embedding video: just copy the link from youtube or Vimeo et violà.
From a couple of days in one instance, I can’t embed video: when I paste the link I only find the url in the page or post (last week everything was working).
As this is the only instance on that specific server I check on another server and no problem.
So I installed a fresh instance of WP on that server: same problem.
I checked apache and php conf comparing with others server and everything seems to be ok.
I also checked the firewall: no error, no alerts, no rules to block or limit traffic from lan to wan. So I tried to connect via lynx from bash to youtube o vimeo: no problem.
Last chance: I try to update and restart server… The problem is still there.
I really to know where to check o how to solve this problem: please any one could be so kind to give me any help? I’m a little bit hopeless.
Thank you so much
A
Wp running on Debian Wheezy with PHP 5.4.45-0+deb7u9, Apache/2.2.22