Dell Alienware Area 51M R2 laptop may fail to display on an external monitor. This isssue is noticed when using a Dell USB Type-C dongle DA200 or DA300 is disconnected and reconnected to the laptop.
Intel Graphics is in power-saving mode which cannot identify the video output source from USB Type-C port. To resolve this, press "Win + P" to switch the display mode manually. This can wake up the video signal again from the USB Type-C port.