If you have a spare cat5 cable around ...swap the network cable and see what happens. Also try a different router port if you have a port available. If you have a spare NIC not used, you can even install a different network adapter in a spare PCI slot and try to re-establish connection through a new NIC as a last measure.
If the laptop is connecting via Cat5 cable, plug the computer into the cable used for the laptop and this way you can isolate it back to the system vs cable, router, etc.