Can't you use warranty?
The issue with laptops is that parts such as the CPU, GPU and motherboard is difficult to properly test, more often than not (IME) stress tests don't reveal the problem, except for cooling issues, and as such replacement or reseating is required. With laptops you need to know how to open them properly and where to find the part. Laptop motherboards cannot be replaced by any random motherboard, it needs to be the exact same model due to the form of it, any other model may not fit.
If you know how to open the laptop, where to find each part and how to reseat them properly without damaging them (this will void warranty), or have a computershop nearby that can do this for you, then troubleshooting can be continued.