E5540 doesn't recognise the built in monitor. Intel HD graphics family

I've been having some issues with my Intel HD Graphics Family, I have a Latitude E5540 with switchable dedicated nvidia GT 720M. Every time I enable the Intel graphics the screen of the built in monitor turns the back light off, making it impossible to use. It recognises the external monitor by HDMI. When connected to HDMI, the built in monitor doesn't appear as available, as if only the connected one exists, but if I disable the Intel graphics, then the built in monitor works. Does anyone else have this problem? I really need some help on this issue since I've searched the entire internet and couldn't find anything.