Cannot duplicate laptop display to external monitor?

So as the title above, it worked for the first time,  then never works anymore. I go to the "Screen Resolution" from the desktop, there are only 3 options: "Extend these displays", "Show 1", "Show 2", there is no "Duplicate these displays", and when i plug in my laptop and the U2414H from a HDMI cable, it automatically extends the display, the  laptop is "1" and the U2414H is "2", i found that the laptop screen was using the intergrated graphics card (intel HD 3000), and the U2414H was using NVIDIA GT 525M. 

I'm using Windows 10 Technical Preview (other Windows versions had the same problems) on XPS L511Z 15.6", i5-2430M, GT 525M/Intel HD3000, Memory 6GB

Hope to hear soon from you all for solutions !!! Thank you !!!