There was a bug that sometimes happens, If you Opened File manager when there was no WiFi connection or resources, then sometimes later when you connect to WIFI it fails to show these two listings. I think there is some way to force a refresh without rebooting , but will have to look it up.
But if you fully power off the n810, then power it back on, connect to the WIFI that your PC is on and while your PC is running, and then and only then start File Manager, you should see the listings for Shared folder, shared media might work, but I'm not sure which Windows Media player you need.