Desk top/ethernet to linksys router not recognizing.

First connect that desktop to linksys with ethernet cable.
then set ip property to network adapter .
Set ip address ,subnet mask and gateway ip to ip property.
Set ip address as the ip of network like if router ip is 192.168.1.1 so set ip like 192.168.1.15
set subnet mask as same as your other computer.
Set default gatway ip as your router ip.
Then you can connect internet.
Let me know if you need more assistance.

Thanks.