MacBook Air M2 15 inch monitor goes out. Opens fine but then goes off.

My Macbook Air M2 suddenly went out. I connected too a separate monitor and all works well. When I open the lid, the monitor goes on but then goes out. I took it to the Genius Bar and was advised that i need a new monitor without really checking it completely. It may just be the cable but I have no way of testing other than what I see. It would stay on for long periods and go out of as soon as I open. I hope somebody has had this problem and has a fix. Thanks in advance.