ROuter Problems with Cable Modem

[R33078]

I have a cable modem. My router d-link Di-604 is connected to my modem by network cable and to my two computers by network cable. Every thing was working fine for a while than all of a sudden only one of the computers is getting internet connection. The router has for four connections and only the connection next to the wan port works. If I move one computer's network cable to the port next to the wan port the internet connection works but not on the other computer unless i connect the its network cable to the port next to the wan port. I hope you understand what i am talking about. Any help would be strongly appreciated.