If you've reinstalled Linux on your server you'll probably find the default settings cause the terminal screen to blank after a certain idle period, which also causes the WMS terminal preview to show a black screen.
To fix this, simply do the following:
Edit the file /etc/rc.local in your favourite text editor
Paste the following line into the file, before any line starting with "exit":
for i in $(seq 1 6); do setterm -blank 0 > /dev/tty$i; done
Save the file and quit. This should now run on startup and prevent your terminal from blanking.