Facebook Video Calling freezes web cam

I am facing an issue when placing video calls via facebook either on Safari or Chrome ( I haven't tried other browsers). The problem is that when I place the call, I can see my own image (video) on the top right corner (small window), but I can't see the other person's video on the big window. Everything freezes by the time the person I am calling accepts the call. The problem does not happen when I place a call on Skype.

If anyone knows how to solve the problem, I'd really appreciate.

Regards,

Diego