Just to rule out a Driver problem, download Driver Sweeper
, pop that and your latest Drivers (straight from nVidia's site I hope) on your Desktop, goto Add/Remove Programs and Uninstall the nVidia Display Drivers.
Restart the PC, at the end of Post hit F8 to get the advanced screen, and select Safe Mode.
Once in open up Driver Sweeper and find and select all ATi and nVidia Display Drivers and PhysX Drivers, clean then reboot normally.
Install the nVidia Drivers as soon as you can and then give it a shot.
Your PSU depending on what version of Akasa's it is, should have 30-35A each rail, as I don't know what one you have it's possible you're running both 6-pin PCI-E's off one rail, and the unit's not drawing enough power.
Try using Molex Splitters off the other leads and see if that improves if you've only got two PCI-E leads, like I said I dunno what exact PSU you have, so dunno what rail provides what lead.