My MacBook cannot start up

If you have no green light there’s a fault on the initial stage of power lines creation, reasons may be a few, a bad aftermarket charger may cause damage to the charging circuitry and the protection circuit. There could also be a short somewhere else taking down main power circuit, it’s pure guess without thoroughly testing the logic board.

It’s not a typical DIY task, your options would be replacing the logic board or finding a lab performing component level repairs, best if with specific experience on Macs.