1. If DLNA streaming media push technology is used for screen projection, the screen will be black after screen projection, which means that the current movie has not been approved for screen projection. Although the screen projection was successful, the media data on the hard disk could not be obtained normally, resulting in a black screen after the screen projection.

2. If Apple's AirPlay or Android's Miracast screen projection protocol is used for wireless screen projection, then the black screen may be due to the firewall corresponding to the screen projection software set on the computer side, so that the screen data of the screen projection cannot be successfully transmitted to the computer side.

3. In the Apple system, due to the limitation of AirPlay protocol, Apple will disconnect the transmission of network data after the mobile phone is black, so when the mobile phone is black, the computer will follow the black screen.

4. If the projector is connected to the computer during the screen projection, it may be because the projection setting of the computer has been turned on "Only the second screen", and the projection picture will be sent to the projector for display, and the computer will have a black screen, which is normal.

In view of the reasons for the black screen after the above screen projection, the corresponding solutions are as follows:

1. In the firewall settings of Mac or Windows system, select Global Turn off the firewall, or find the incoming connection settings of the corresponding projection software, such as AirServer software, and set them to allow incoming connections.

2. When using Apple's mobile phone to project the screen, it is recommended to set the automatic screen lock to "Never" in the "Display and Brightness" settings.

3. When connecting the projector, you can call up the "Projection" setting through Windows and P shortcut keys, and switch the projection to copy, so that the computer screen can enjoy the same video output signal as the projection screen, and avoid the situation that the projection has a picture and the computer screen is black.