All users with the same ip address, why?

Hi guys, I do not know why, I can not understand it at all since I did not make such strange changes to my script ... but ... I find that every visitor, so every one of my users has the same IP address.

This causes me malfunction to my site, because voting systems and counting visits depend on IP addresses.

(I tried to install a copy of my script into a subfolder, but everything works, but users have different ip addresses.)

I ask you maybe you can understand the cause,
I do not think I have touched anything on config.php or anything else.