"Failed CPU Test"
The PSU suggestion is a GoodOne... also, so is OverHeating. You may not have adequate cooling for the CPU and/or Case and it slowly heats up when under intense apps like Gaming (100% CPU Use). The overheating could be caused by the above or it is struggling to get enough "Juice"- PSU... The XP2000+'s are power hungry. Either way, an overheated chip would generate the above error.
I would start with the cheapest- add cooling and see if the situation changes. If that doesnt work, I would swap the PSU.
GoodLuck!