If your WAN link and connections are fine but unable to open any link in an intranet. What maybe the problem & what is the solution for it?

Make sure first, the reachability between Intranet to WAN Link Router should be ok.

Then check the Firewall rules for  ports HTTP, HTTPS , should be open from  Intranet to  outside Internet.

Check local DNS working or not, ISP DNS should be defined .

Then Check the proxy, may be blocking the ulr link to open for Intranet, if required, create the rule for the same.

Make sure the host IP and Gateway is correct if in case having router or firewall connected with LAN and  WAN or if its using modem directly connected to the host ensure that is their any public ip is assigned statically in host.

check IP on host and proxy setting 

need to check any firewall or any closed ports