Power supply failure. A capacitor was actually blown in the original psu.
Very easy. Knowing all the basics and how all the components function is a definite plus, but truly not necessary for this task. It's all separate units, about the same as replacing, say, a spark plug on your car or truck. Just remove the faulty part, replace with the new unit, plug, and play.
Be sure to line those pins up on the psu during installation and the top mounted power bridge pins. Other than that, it's an easy task.