Keyboard not starting when power button pressed

Was working fine until a few days ago. Always had a loose connection problem near the dc input but that used to be fine and it used to work after moving the power supply a little bit here and there.

Verified that the power supply is not the problem by connect the 9v dc input from the battery end.

Now whenever I try to switch it on the lcd backlight comes on but the keyboard itself doesn’t start. As long a the power button is held down the backlight is on but on releasing it switches off immediately.

For a few days the backlight would stay on even when the power button would be released and sometimes the keyboard would actually start and then go back to a COD backlight only mode. Now even that doesn’t happen

Any help would be appreciated