Also shine a bright flash light at the screen at different angles and look at different angles.
This can sometimes tell you he difference between a failed video controller
and a failed "inverter" for the florescent backlighting for a typical LCD
screen (unless you KNOW your model has an LED backlight screen)
You can also connect an external monitor, but you typically need to hold
down the "Function" key (sometimes labeled "FN") and one of the other
F-keys (F1-F12) to switch to the external monitor.
The issue is that "Black screen" on a notebook can be from either of these causes... but there is another cause.
That FN + F-numeral key combination can turn your perfectly normal display OFF.
on many computers (the Dells and HP's that I have now plus an older gateway I gave away years ago) that key combination typically scrolls through four choices
the built-in Display (normal state)
Both displays ON
(and on only some notebooks)
Both displays OFF