HI10 Plus (LQ64G42161103042) couldn't power on, the led does not blink

After 5 years of trouble-free use HI10 Plus (LQ64G42161103042), the tablet suddenly refused to turn on. It was plugged in the charger, I tried to switch on it without success. when I unplugged it from the charger, LED started flashing very fast. I turned it off the on/off button and it went off forever. I have been pressing the on/off button for a long time, nothing happens; when I connect the charger, the led does not blink. I opened the tablet, disconnected the battery and recharged it to 4.2v with external source, again it can’t be turned on.
What can I do from now on? where could the problem be? Is it possible that there is a problem with the BIOS, although I have not done any BIOS interventions? can i send the board for repair? or order a new one if possible?