Is the router between your Lan and the server ?
In that case you are probably right.
If not, have you set up the server to a specific ip-address, subnet and to serve DHCP-leases ?
In other words, can you access the server at all ?
Are you trying to connect with the domain name, servername or with the ip-address ?
If these questions don't ring any bells, please report back with a bit more specific problem description.