What is the brand and model of your power supply unit?
System Power Supply Requirements for a single NVIDIA Reference Design GeForce GTX 1070
• NVIDIA specifies a minimum of a 500 Watt or greater system power supply. (Minimum system power requirement based on a PC configured with an Intel Core i7 3.2GHz 130 Watt TDP processor.)
• the system power supply must also have a maximum combined +12 Volt continuous current rating of 28 Amps or greater
• the system power supply should also have at least one 150-Watt 8-pin PCI Express supplementary power connector. There are some non-reference design cards that require one 75-Watt 6-pin and one 150-Watt 8-pin PCI Express supplementary power connectors (e.g. MSI GTX 1070 Gaming X 8 GB).