If the laptop had been working normally up to this point and suddenly stopped, a common issue is that most laptops have a key sequence for changing the video output from the built-in screen to an external monitor. Determine the key sequence for your laptop via Google or the documentation and see if the video output was accidentally changed from the internal screen.

Otherwise, if the laptop will not power on at all there is another issue, perhaps power or hard drive related. Have the laptop diagnosed by a local tech or the manufacturer's tech support.