system unstable after adding second video card

[Eddie A]

Hi Guys ... I need your expertise on an issue with a new pc im putting together.

i7 6700 K stock
Asus maximus viii extreme with latest bios
4X 16GB hyper x predator ddr4
Seagate 4TB drive for testing
2 x GTX 1080 iChill X4 edition factory OC'd
Psu thermaltake XT Gold 1475 watts
Win 10 pro build 1511 (64 bits)
Geforce driver 368.39

System runs fine until i add second gtx card. I start experience random hard reboots from desktop or when windows is loading. It can happen every two minutes or every 15 minutes.
Psu just clicks and pc reboots.
No memory dump. Event viewer shows kernel power code 41.

If i manage to boot i can run benchmarks and the pc never restarts during benchmarks. Only from idle or when booting. It happens just when i click on a random icon on the desktop or an item in the start menu. Sometimes without me clicking on anything. But never when running benchmark.

When one card is installed alone its stable. With any of the cards installed alone so i know the graphic cards are not the problem.

I replaced the mother board with a Gigabyte z170 SOC Force but the symptoms remained the same.

I replaces the Ram with 2 x 8GB sticks but that didnt fix it either.

Can someone give me an idea what is wrong ?

I thought about the Psu but under load system is stable.

I really dont know what to do anymore ...

 

[Eddie A]

Any ideas guys ?

 

[Eddie A]

Thank you for your many replies. Problem solved.