Black screen, all cables & power ok

@padmanabhan what power output is ok. You need to tell us what you have checked since this is a bit confusing. If you have power to the monitor but the power LED doesn't light up, the issue is a bad power board. You will have to disassemble your monitor and take a look at the power board etc. Check for any damaged looking component etc. you can always take some well-focused pictures and post those with your question. that way we can see what you see.

Use this guide Fix Dell U2415 Flickering Display to get to the boards.

Adding images to an existing question