@rajwadkar07 remove your power adapter, your battery and your RAM. Then hold down the power button for something like 30sec. After that reinstall the power supply only. See if it powers up. Errors like this can be caused by bad memory modules, bad power supplies as well as bad batteries. Of course you can never rule out the power button or motherboard. Check the AC adapter first. Make sure that it provides proper voltages to your computer. [https://www.parts-people.com/blog/category/dell-inspiron-repair-manuals/inspiron-15-3521/|Here is] an online service manual that will help you to work on your computer.