I have 3 monitors attached to my graphics card, a Nvidia 650ti, and in my new installation everything seemed to working fine except the screen saver.

When the screen saver was activated then 2 monitors was flashing on and off and the last monitor on the HDMI connection was turned off and would not get alive when it went of screen saver mode.

I found out when I configured the graphic card to use separate X screens the problem was solved.

To do that:

1. Start the nvidia-settings and under 
   "X Server Display Configuration"->Configuration 
2. select "Separate X screen (requieres X restart)" 
3. Also Enable Xinerama under "X Server Display Configuration"

You can’t just apply these setting and you will have to save it in “/etc/X11/xorg.conf” configuration file and restart the X-server.

If you don’t have xorg.xonf file then one can be generated by running:

$> sudo nvidia-xconfig

I prefer to reboot after this change but it can also be done by restarting the X-server.
On Kubuntu (save everything as your session will be killed):

$> sudo service lightdm restart.

Now once the X-server is restarted you might have the same problem as I do: Only English keyboard layout.

The can be fixed by either change the xorg.conf file or by running the command:

$> setxkbmap -model pc105 -layout dk,us -option grp:alt_shift_toggle

This will setup a 105pc keyboard and have both Danish (dk) and American (us) keyboard layout and to change between the 2 press the <Alt> and <Shift> simultaneously.

This will of cause be reset every time the computer reboot so I added the command to (if you are running KDE as on Kbuntu):

/home/<user name>/.kde/env/setlocale.sh