I doubt anyone will be able to help you given the very sparse information you're providing.
What is the OS. e.g. Distribution, version?
What is the VNC server, e.g. TigerVNC?
What are you using for the VNC client?
Describe how you connect the VNC session, e.g. using secure SSH?
Is the VNC server running in Service or User mode?
solved by 'restart' VNC session from remote server
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Prior to the "restart" did you check the $HOME/.vnc/*.log file for the vnc session?
That file may hold clues as to what was actually wrong.