Both pc's need their own IP addresses. Have you trie running this troubleshooter?
Sometimes this works..
Shut down both computers; Unplug the router; disconnect the desktop's ethernet cable if connected this way; Plug in router; Boot computers.
Surface Pro (2017) vs Surface Pro 4
Where HTML5 is headed next
MacBook Pro v Surface Pro 5
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.