You can face many issues in the connection between a projector and your computer. Most of the time, the issue is with the wifi connection. If any one of the devices is not be getting a proper wifi connection, it will not let the screen share through the projector. If you are unable to see the screen through the projector, then you must first check the wifi connections on both devices.
If you have a wired connection between the computer and a projector, still you can face the same issue. But for this case, the wire connection should be fixed. Sometimes the wire between both the devices is loosely attached. You must refix the wire to establish a connection and see your computer screen through the help of a projector.