Did I break the laptop now?
Wawawa What? Did you plug the headphones into the USB socket? Take it out again, then the laptop will start again. Otherwise you might have damaged the motherboard.
It may be that there was a short circuit
This could have been damaged either the USB controller or the whole motherboard
Did not put it all in
Can I fix the mainboard?
Maybe you destroyed the USB controller. But it is also possible that your motherboard has taken damage. Is it an old or a new laptop?
Arrives completely on the laptop.
If that were really the case, a new laptop would probably pay off. Most laptop CPUs are soldered, which means that they will be replaced immediately.
Asus gaming laptop, would be 3 years old now
Contact Asus at best and agree best MB exchange. It costs about 300 euro.