@dhirajg start by removing your battery, your AC adapter and your RAM. Then push and hold the power button for 30 sec. After that just install your AC adapter and see if it comes on. Try the same with your battery. If it does reinstall your memory and see if it still comes on. Failed memory module could be an issue. If it does not you will have to disassemble your computer and check the DC-jack in. Attached is the schematic for your computers power management and should help you tracking it down. You will of course need a good multimeter to check on this.
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