I have 2 7990's and my temps stay around 75c but the system shutsdown after about 30 or so minutes and when i go to check on the temps or open application. I am using GUIMiner, /having issues getting cgminer working on windows 7. It doesnt recognize my cards.
So what happens is I go back to the computer and open a browser / gpu temp monitor and when I bring it up it shuts the system down. Am I putting too much of a load on the cards ?
I am getting 1.3 mh/s per card (7990).

Computer setup :
Win7
ASUS Crosshair v Formula-Z AM3+
AMD FX-9590 Vishera 4.7Ghz
2x7990
2x R9 270x
32gb Kingston HyperX Beast 32GB DDR3 2133
240GB SSD
1350 enermax platinum
additional 1200w psu.
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Spare ATI 7850 to use for windows non miner card. Not installed

Thanks Everone for your advice / input.