Start button flashes but laptop stays off?

My laptop suddenly stops working and the start button only blinks every 3 seconds, what could that be?

Have already taken out the battery and pressed the start button to unload completely but after inserting nothing has changed

So first, your laptop will not be completely discharged when the battery is out, because the BIOS is still supplied with the CMOS battery, but that does not solve anything yet. Maybe one of the measures mentioned here will help you:

https://h30492.www3.hp.com/t5/Notebook-Hardware/Laptop-Startet-nicht-Power-LED-blinkt-3-mal/td-p/506465

https://h30492.www3.hp.com/t5/Notebook-Hardware/LED-blinken-kein-start/td-p/5679

https://www.computerbase.de/forum/threads/laptop-mainboard-kaputt-3-mal-led-blinken.1662881/

I would assume a memory defect, so something hardware technical, but you should try the solutions suggested times and visit no repair store repair.