Hello,
This issue may happen more often if you have changed networks, or experienced a drop to your connection and had to re-establish it.
When this happens, the OS X Finder may still maintain its list of available shared computers, when the system has lost the network association with the system. In cases like this, the Finder should update to reflect a new link to the shared systems, or remove them if they are no longer available.
To fix this problem, you simply need to relaunch the Finder, and it will re-populate the list of shared devices. Hold the Option key and right-click the Finder icon in the Dock, then select “Relaunch”.
