Mac Pro 2007/2008 fresh Snow Leopard install with GT120 graphics card?
The Apple NVIDIA GeForce GT 120 Graphics card is not compatible with the 2007/2008 Mac Pro, so in order to do the fresh install you will want to remove the GT 120 and re-install a compatible graphics card that will work with the 2007 / 2008 generation of Mac Pro.

As noted on Amazon the following system requirements are noted for the Apple NVIDIA GeForce GT 120 Graphics card.


  Product Features
  
  
  Requires Mac Pro (Early 2009 with 1066MHz DDR3 memory) with PCI Express 2.0 slot
  Requires Mac OS X v10.5.6 or later