@inlerah start by removing the battery, the AC adapter and the RAM then hold the power button down for a while. Replace the AC adapter and see if it starts up. You also want to try a USB keyboard and see if that makes a difference. If not then I would suggest that you replace the RTC battery first and try to start it up after that. Use this guide Dell Inspiron 11-3147 CMOS Battery Replacement for that.
Any of this
Gate A20 failure
Super I/O chip failure
Keyboard controller failure
would require boardlevel repair and for that you need to let us know what exact motherboard your computer has.
@inlerah have you tried a different memory module? You do want to rule out that you have a bad module. Your motherboard should have a few numbers silk screened on the board. Just give us those numbers or post some really good pictures of your board with your question. You can use this guide iFixitでの質問に画像を追加する方法 to do so.