have you tried assigning the problem pc a static IP address, subnet mask & default gateway within the dhcp scope instead, just to see if you can connect?
How many "other" pc's are on this network including problem pc and server? Perhaps the dhcp server (router) has been configured in the past to issue dhcp addresses but only 5 of them or another small #.
when using static it says conecnet but can't ping or be ping and dos not show up in attached diveces in the router, 3 servers, 6 pcs, 1 mac, problem pc and nokia phone, the router is set to use a range of 225 ip address.