http://www.amd.com/us/products/desk...5850/Pages/ati-radeon-hd-5850-overview.aspx#3
AMD are recommending 500W themselves, you are still suggesting a new psu as I had already said. I think that is a bit premature, i'm leaning more towards driver or a corrupt installation of wow if another game/demo is running ok.
The OP seems to be trying to run before he can walk so to speak. I would install the new drivers and run the 3dmark program. Let him post back what he finds.
*edit* explain what you mean by upgrade? What is old and what is new? Did you reinstall windows for this mobo? If you didn't that is highly advised. Saying that windows asked to be reauthenticated leads me to think you didn't