It's not the mobo. Your power supply is deficient. Buy an 800 Watt Antec or 800 Watt Corsair. And before you tell me, "Well, I have a 1000 Watt XXXX Brand" bear in mind that the ratings on power supplies are pure fiction.
I do in fact have an Antec 1200W power supply...here's the model:http://www.antec.com/Believe_it/product.php?id=MTc1Nw==
Based on the following thread, it seems I'm not the only one experiencing trouble with this mobo:http://vip.asus.com/forum/view.aspx?id=20110211072855742&board_id=1&model=M4A89GTD+PRO%2FUSB3&SLanguage=en-us&page=1
I have opened an issue with ASUS. But the question remains...I'd like to hear from people with a dual 5970 setup with a socket am3 mobo, which specific model are they using?