Hello and welcome to JustAnswer, I look forward to assisting you today. There are a couple of things I would like you to try. If you have a regular computer monitor, try plugging it in to your Gateway to see if you can see your desktop. If you don't have one, shine a flash light close to the screen and see if you can see any of the icons. Let me know what you find.
Put the light right up against the screen and look close. It may be hard to see.
Okay, and the screen if completely black then correct?
Okay, one thing you can try. Remove the battery and unplug the power supply if it is plugged in. Press and hold the power button for about one minute then power it back up and let me know what happens.
Look at the top function keys and see if you can locate one that looks like a little monitor. Try pressing and holding the function (fn) key then press that F key to see if the screen will turn back on.