Hi! I just bought a Dell Inspiron 3542 with an i7, 8 GB RAM, 1 TB HDD and video card nVidia GeForce GT840M 2MB.
I have a problem trying to switch my monitor from the integrated video card Intel(R) HD Graphics 4400 to my nVidia GT840M. I must mention that I am up to date with all drivers, tried to switch the PhysX and the Global Settings in the nVidia Control Panel but nothing works. Tried disabling the Intel 4400 from device manager, but then I can't open nVidia Control Panel. I don't know what to do anymore. 
It simply doesn't move!
If someone can help me, please!