Cubase 6.0.7 with huge CPU spikes with Focusrite Saffire 40

Hello all.

I recently reinstalled my DAW since I wanted to have a “clean desk”.
After reinstall I noticed huge and nasty CPU spikes while playing a
project in Cubase. My interface is Focusrite Saffire Pro 40 and there’s
a firewire connection between DAW and interface. I’m aware of the FW issue
with Windows 7 where you must use legacy driver, what I’m using anyway.
It doesn’t matter. When playing a project, system freezes for a couple of seconds,
then it tries to continue playing and freezes again. When capturing performance
data, it shows huge spikes with CPU and disk IO. I copied the project to another
disk but it doesn’t matter either. When playing a song from Spotify or from Windows
Media Player, it works just fine. Windows logs doesn’t show anything strange and
Windows itself is working fine. So problem is probably within Cubase -> ASIO -> Focusrite
Saffire.

This didn’t happen before reinstalling. I’m using also IK multimedia software synths,
Superior Drummer 1.0 and Waves Renaissance Maxx native-package. My DAW is
Windows 7 64 bit and I’m using also 64bit version of Cubase 6. Does anybody know
what is causing this?

Br, Sampo

UPDATE:
I found the root cause. Only thing I changed during reinstalling & upgrade was the graphics card.
I wanted to upgrade from traditional generic ATI card to Quadro FX-series card and after several try-outs
(includes reinstalling cubase & asio driver / running system without asio, firewire cables removed etc…)
I realized that my power supply was running out of power! I switched back to my old graphics card and everything
started to work smoothly.