Why won't my desktop and laptop communicate?

I have a laptop and desktop. I wanted to transfer some files through an ethernet cable via my router so I plugged the cable into my laptop and then into one of the ports on my router. I used to do this all the time and transfer files but now, when I open the network on either pc, the other pc doesn't show up. I don't know which services should be enabled to allow the pc's to find each other