Hi @Ms Mandy,
Your model laptop has not got a RTC battery.
According to [https://support.hp.com/au-en/document/c01732674|this], a ''5.3 (blink) pattern'' indicates a problem on the ''System board'' - ''The embedded controller times out waiting for the BIOS.''
You say that “I tried every method. I can't fix this.”, but this doesn’t say what exactly you have or haven’t tried
Have you tried disconnecting the ''main battery'' from the motherboard and then pressing the Power button for 30 seconds, to try and reset the BIOS?
''If you haven’t:''
Disconnect the charger if connected and then open the laptop and disconnect the main battery and press and hold the laptop’s Power button for 30 seconds and then release the button. Reconnect the main battery, reassemble the laptop, connect and switch on the charger and try to turn on the laptop.
Here’s the [http://h10032.www1.hp.com/ctg/Manual/c05527168|maintenance and service guide] for the laptop, taken from this [https://support.hp.com/au-en/product/hp-pavilion-14-bf100-laptop-pc/16842295/model/19955239/manuals|webpage]. Go to p.29 to view the necessary pre-requisite steps and then the procedure to remove the battery.
''If you have:''
Then you have a motherboard problem