The whole machine turning off could be a sign of a bad PSU, considering that the motherboard is telling you that's happening is pretty convincing evidence. Return it to the store for a refund and get another (smaller as well, 850W is overkill for a single card, only need 600W).
As for the display randomly failing.
That Nvidia driver stopping and starting means you have an unstable overclock, you'v probably upped the Core too high without enough Voltage to sustain it. Set it back to stock speeds and do it properly. Bump the core by 25Mhz, run Furmark for a min or so, bump the memory by 25Mhz, run Furmark, etc, etc... Until the the driver starts failing again or you get artefacts (lines, dots, weird colours within Furmark). Then you can decide to up the voltage to stabilize it and clock higher or back off the speeds and stay within stock voltage settings.