Well i don't know if you got it figured it out by now, if you did good , if not then there are few reasons and solutions for over heating CPU and automatically shutting down.
- when you play games continuously or do some kind of encoding stuff, the processor is engaged, normally processor uses only 50% of its capacity, but if you do high end stuff or play high graphics games, a lot of processor power is used and heat builds up in the processor and near by motherboard. But to counter this processors come with fan mounted on heat conducting metal object to dissipate the heat.
Likely causes are since it is a new computer :
1. The CPU fan is not working efficiently, usually it should spin at 3000 rpm at full loads, but in your case it might have been spinning not more than 1200 rpm.
2. The heat sink material was not properly installed during the processor installation.
3. BIOS settings might be limiting the CPU fan to work at full potential due to acoustic settings.
As a result of which the CPU overheats and temperatures goes up to 85 to 90 degrees Celsius. So as a safety precaution the motherboard is programmed to shutdown the power after the temperature crosses the safety limit of working environment because that much heat can damage parts of motherboard.
1. 70 % of the cases in which motherboard automatically shuts down the power, there will be probably some damaged caused to the motherboard. So check first if your motherboard is fine and doing good.
2. Upgrade your CPU fan with now a days available highly efficient liquid cooling of air cooling solutions for the CPU. In which case your CPU temperature wont rise above 60 - 65 degrees Celsius at full load for even 24 hours and the idle temperature would be around 38 - 45 degrees.
Hope it helps