Projectorsprojector showing no picture

Hello! Thanks for all your suggestions, and sorry for not getting back to you sooner. I tried a bit more, pressing the “computer” button on the remote (which presumably cycles the input between “computer1” and “computer2”. That did not do anything, but then I connected the cable to the “computer2” socket. This immediately gave me a picture with the computer going to “extended” mode automatically , then I could set it to “mirror” and I now have the picture (both in “computer1” and “computer2”, direct and through the box.)

My problem now is the keystoning. Pressing the “keystoning” button on the remote does not do anything. I can find it on the menu, but again the picture does not change.

I am afraid I can’t see either the model or the serial number on the projector. It is an orange Promethean, and it would seem the numbers must be on the (upturned) bottom side  where I cannot see.

Any suggestions what I could do here? Thank you again for your help!