can’t surf

I am the administrator for a small network using Cisco 3600 routers. I have one central router connected into a WAN with four routers comming off the central router.
Each router is renning two eathernets. None of the clients can access any sight on the www. When they do a trace rout on yahoo.com (for example) they get out through my network and through the WAN we are connected to. It seems like everyone is getting out to dofferent places on the www and then timing out at around 16-18 hops. Is there anything in the configuration of my routers or the WAN routers that could be causing this. The WAN administrator assures me there are no blocks on any of my addresses. I am stumped please help.