Hey Guys, and before I start - my english is not the best

I have been trying to get my rig to run since days..
When I install Windows 10 / Ubuntu - Every Card gets installed and works - But as soon as I try with Claymore to mine, the PC freezed..
I already tried Mining with other Software or a other System, but always the same problem.

My Hardware is:
6x VTX3D AMD R9 390 GPU
ASROCK H81 BTC R2.0 MOBO
INTEL CELERON G1840 CPU
HYPERX FURY DDR 3 4GB 1333MHz RAM
SAMSUNG 750 EVO 120GB SSD
3x COOLER MASTER B700 PSU
PCI-E Riser Powered

The Mobo + CPU + 2 GPU  -- POWERED RISE CABLE + 8+6 = 1 PSU
2 GPU = 1 PSU  -- POWERED RISE CABLE + 8+6
2 GPU = 1 PSU  -- POWERED RISE CABLE + 8+6



.. The next Problem is - when I stick my gpu directly into the second x16 Port - everything works with mining.. nothing freezed - when i put a other card in - both work.. but at 3 cards - nothing works :/

I have no more ideas left..