When i try to join CS(Counter Strike) servers with Steam i loose my internet connection so i though maybe i should disable NAT in my modem but every time i do that i loose my internet connection, why PLZ HELP!!!

You cant disable NAT, because then you no longer have an IP address, and your modem is no loger routing.

NAT must be turned on. It is not your problem.

This will give you more info about NAT http://en.wikipedia.org/wiki/Network_address_translation

If you are using a router, you probably have multiple devices connected to your network and in that case NAT is important. Why were you turning it off?