I have a Dimension 4600 Desktop.  Did a system restore to factory conditions, but now the computer will complete startup.  It gets a blue screen of death due to a loop in the nv4_disp driver (Nvidia).  I remember having to fix this not long after I got the computer.  The problem now is that I also can not get the computer to startup in any version of safe mode.  I get a message that system setup is not complete. 

Any help would be appreciated.