So, you need to wait for a while till the content loads up.
When a user tries to stream media content in the 4K UHD resolution, the chances of a black screen or the flickering screen becomes higher.You must press and hold the “Up” button along with the “rewind” button in the remote of your fire stick for at least five seconds, this will provide you with the option to change the resolution.
You must check and unplug any other connected device with your TV.Try using the different HDMI cable extender to connect your fire stick with TV.Make a selection for the working HDMI port through which you have connected your fire stick to the TV.Some other measures you can go with to get rid of black screen on Amazon fire stick: