So just about totally finished a new build...i7 4770 with standard Intel heatsink, GTX 780, 8 GB ram and fresh Windows 10 Pro install using a Gigabyte H81M S2PH board running the latest BIOS. All up and running, decided to do a couple of benchmark tests, used 3DMark Vantage first up, got maybe 30% through the test and heard the video card's fans ramp up real hard, went to look and noticed no video output. Checked whatever I could; turned the PSU off. Had a look inside case; all appeared normal...restarted left it idling for some time used HWInfo to check temps, all looked OK. Installed 'Heaven' benchmark, started it up...similar result...loud fans and no output to screen...hmm. Turned PSU power off again, changed the 780 to a known working 970, restarted and once in Desktop decided to try to monitor using AIDA64 Stress Test and HWInfo in unison to try to watch the temperature readings...no sooner started up that got a warning about CPU throttling due to overheating...temps were up to 99°C. What I'm struggling to understand is if the CPU temps are the cause...why is it resulting in a loss of output to the screen and causing the video card fans to ramp up to full speed, rather than just shutting down the PC? That AIDA64 Stability Test has been running now for over 25 minutes with the CPU temps about the same, throttling of CPU down to 25% or so, but system still running. Where do I start? Is it simply a case of CPU cooling with the basic Intel heatsink being totally inadequate...or do I need to try other tests/methods to determine the issue so it may be corrected?