Killing VNC Process Manually
Try running
ps -ef | grep vnc
to see which VNC services are running.
As @bob has mentioned use the command -
ps -ef | grep vnc
It will list all the vnc related process that are in running state.
So note down the PID of the process having the name
Xvnc
And execute the command kill -9 <PID of Xvnc Process(es)>
I will kill the VNC server.
Then restart the VNC server and think are back.