why do you think that multiple 5970 fry motherboards?

[walkingcat]

It's not connected to the PSU. The extra power connectors on the cards are simply not sufficient to power the card. Therefor the cards draw excessive additional power from the PCIe socket (path of least resistance), violating the specifications and causing the motherboard to take damage.

The solution to avoid frying your motherboard is not using such cards.

Thanks, will this still happen if you only use 2 5970s?
I apologize if this is a stupid question. I'm a beginner.