when I play with high or ultra settings, the monitor goes black and says the video signal is lost. The sound makes weird noises and I have to restart the PC with the power button. It happens especially when the system is working hard, e. g. always when I enter the balkony in the very first room to take a look at the landscape. With medium settings it seems to be ok so far and I don't have any problems with other games or benchmarks. my system:

CPU: Intel Xeon E3-1231 v3
GPU: EVGA GeForce GTX 970 SuperClocked ACX 2.0
RAM: 16 GB DDR3 1600
HDD: WD Blue 1 TB,
Windows 7 (on an SSD)