Per question in your PM on rather you should get a new CPU, I believe there are a couple of things you can try before spend the money if you have narrowed it down to where the problem seems to be.
For your lockup problem, I would check the CPU heat-sink fan to see if the bearing going out. When powered down, nudge the blades with a toothpick. If they jiggle to a stop, all is well. If they coast to a stop, the fan's bearing is dry and needs a relube to come back to full health. Easily done by peeling the label from the back, and maybe find a small rubber plug. Under that is the bearing. One or two drops of light machine oil such as 3-in-1 worked into the bearing by hand for a minute will do the trick.
Another is reapply thermal paste.
It is really a dilemma you have to decide for yourself. Let's say, if you replayed the CPU with the same model and then found out it is the mobo; you may want to upgrade the mobo instead of getting the same model which leads to the possibility of ending up with a better CPU. Which means you waste money on the previous brand new CPU. After that, you may learn that the problem is really the not so good quality, unstable PSU. And so on... HaHaHa!!!.. to the point you would wish you had never spent a penny trying to repair it instead building a brand new and better one. Just kidding. Wish you luck. Let us know how things go.
