Notebook And Desktop Running Windows 7 Can't See Each Other?

Both run Win 7; both use lan conections to the same router (Linksys 310N). Both get to the internet. And while the network map shows both of them, they are both unreachable. BUT NOT ALWAYS. Sometimes, maybe after several hours of uptime, they can access eachother. And the printers, which are wired into the desktop, then can be used by the notebook. BUT not always. Like now, all my printers are "offline" as far as the notebook is concerned.There are also wireless connections but currently I don't use them. Both machines are on the same-named connection. Homegroup doesn't work at all on either computer. I would really like to print from the notebook. All the printers are wired into the desktop. All are shared. Yesterday I could print from the notebook. On occasion, the homegroup shows both computers but hasn't for a while. In File Explorer, on the notebook, not even the notebook appears under the Network icon.