what happens if my brand new ryzen 1600x reaches 120c? and what happens if after it reaches that, i shut down the computer to let it cool and then it wont turn back on?
It can't reach 120*C, as there are throttling mechanisms in place as well as hard shutdown safety triggers before it hits even 100*C. Turn off or unplug your PSU for a minute or two and it'll turn back on. Also make sure your cooler is installed properly.