Sapphire 7850 2GB - 511 temp C error

[Muffnz]

Hi. I have mini mine-rig with 3x7850 Sapphire 2GB. Mother Gigabyte P55A-UD3, 6gb RAM, i5-760, Corsair 850W.
After 10-15 min when i start mining scrypt, my computer freeze, and one card.have 511 temp on cgminer 3.7.2
I have last non-beta AMD drivers and sdk 2.9
On my GPU i can manual switch bios. But i have the same problemon another bios.
Two GPU in 16x on mother and one with riser with con power supply
What can i do with that shit?