Most desktops do not have wifi on the Mother Board as laptops do. You have to purchase either a USB wifi dongle or a pcie wifi card. Or you can plug the desktop directly into your router/switch using a cat 5 cable
Did you check router's settings?
You can always set up the router yourself. Confidence in this added me this site 192.168.l.l login. Everything is detailed and shown in the photos. I'm sure that everything will fine. It's very simple.