Hello and thank you for choosing justanswer.
When changing the screen resolution, it wil ask you if you want to keep the settings, and if you don't select yes, or no within 15 seconds, it will revert back to the previous resolution settings.
You might be able to get something on screen with an HDMI cable. The small cable is just called Mini HDMI Type A.
Start the laptop in safe mode to fix the resolution issue.