Win7 X64 Driver Signing driving me mad!

Hey folks. I am hoping someone can shed some light on a long term frustration.
 
I have 3 laptops that I use for music production. AlI are HP i7's, though different models. I have just done a spring clean with clean installs of windows 7,  device drivers and Sonar on all of them. On two of them the process was relatively painless. On my studio computer, however, none of the device drivers would load unless I enabled windows test mode and individually signed each driver using NGHQ driver enforcement overider. All were formated and set up using the same version of windows from the same install disc - only the serial numbers varied. All were loading identical drivers. Does anyone happen to know why this would happen on a particular computer?
 
Taa:)