There are indeed some reasons why projector says no signal. The reasons to it get further elaborated as you are following.
Why projector says no signal?
It is surely very frustrating while we are in the middle of a video and suddenly the projector brings a popup of having no signal. This has been a reoccurring issue and everyone has faced such a situation. There are reasons for it which we are now looking at.
Problems with the cable
Connectivity issues with the cables sometimes lead to the occurrence of such a popup on the projector. It can be that there have been some issues with the cables that have stopped the projector from operating. It is important to check the HDMI/VGA cable.
Problems with the computer
Projectors are mostly connected to computers. If the HDMI cables of the projector are perfectly fine, there might be some issues with the computer with which it is attached. Sometimes some programs on the computer like the output to video settings have not been connected properly, stopping the signals from reaching out to the projector.
Problems with the projector
Perhaps the source button on the projector has not been properly functioning and this has brought in the occurrence of this issue. If you press again on the source button, it cycles the projector to the HDMI input properly. And sometimes there may be other internal issues with the projector as well. This can be resolved by pressing the reset button on the projector. Resetting clears away the lingering issues mostly and makes the projector function work like before again as well.