Three beeps upon startup

@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 Adding images to an existing question to do so.