AMD Fx-4100 stuck at 1400 Mhz

Solution
There might be a 4th reason:
Your cooling isn't sufficient for it. Be it the actual CPU cooler or the case cooling to get the hot air out.

CTurbo

Pizza Monster
Moderator
You are experiencing thermal throttling. There are three main reasons that would cause this.
Your motherboard could be faulty.
Your motherboard could just be super cheap and is not getting enough airflow.
Your cpu heatsink is not installed correctly.