Hmm, I was thinking about the PSU, but if it was the problem, then the PC would have never ran normally. And the rig certainly runs nice, but sometimes it just refuses to boot Windows, as I've said. When the no-boot bug happens, there is no BIOS beep, if that's what you mean by case speaker .
Thanks
What do you mean by run nice exactly? As an example, have you run any tests such as
http://www.ocbase.com/ ? That tool will help you test your power requirements/efficiency and load on your GPUs.
153w per card at the wall
http://forums.evga.com/tm.aspx?m=2106947~460w total for the cards. Is the rest of your system falling under spec? What is the PSU efficiency? If its 80%, then yes you are most likely falling short on your power requirements