I have a Raspberry Pi 3B+. For several months it worked perfectly fine, but one day it just stopped booting and only getting to the red LED. I've tried buying a new microSD but the same behavior keeps happening. Is there anything else I can try or do I have to buy a new Pi?
There are many experiences about why a Raspberry Pi don't boot anymore. You will find a wide collection about reasons at the official Raspberry Pi forum. Following the The Boot Problems Sticky I'm sure you will find what's your problem and if you have to purchase a new RasPi.