Hey Lei,
In your application, you are using a call library function node to call a function in the user32.dll. Unfortunately, I am not extremely familiar with that particular .dll. However, in order to use this function, you need to know more about what information it is expecting. Can this .dll be used to turn off a single monitor? Is there a certain input the .dll needs to differentiate between your primary monitor and secondary monitor?
Unfortunately, you will need to know more about the .dll you are trying to use. Once you know what information your .dll requires, implementing in LabVIEW would not be difficult. Perhaps www.MSDN.com would be a good place to get more information about how the .dll works and how you might use it to turn off a single monitor.
Purhaps there is another .dll that would be better suited to accomplish this. Is there a .dll provided with your video card/driver that could be used?
