Without some very expensive equipment, the only way to figure out what part is at fault is to use the process of elimination, which entails the swapping of parts.
Everyone's zeroing in on his PSU, and that could very well be true, but he doesn't appear to have a POS PSU:
There's only one 700 watt PSU from them, and it's the
GP700A-HP, made by High Power. (the HP column) It *should* be an okay PSU. It is rated for full power at 40°C.
What I'd be concerned with:
- VRM's on the motherboard getting too hot. That motherboard may not have been designed with a tower cooler in mind. I would actually wonder if a top down HSF, like the Phanteks PH-TC14CS or the Noctua NH-C14S
(reviewed here at TPU:https://www.techpowerup.com/reviews/Noctua/NH-C14S/) might be the better choice?
- Quality of electricity. IIRC, someone else was having problems with an ASUS motherboard and it was related to the "ASUS 5X Protection". If your power delivery is not very good, that may be causing problems. Worst case scenario, you'd have to get a line conditioning UPS.
OP, what fans do you have in your case and how they are configured?