I have a 420 MX, and use the 96xx driver. I also always got a black screen when starting up. What worked for me was to out-comment some lines in /etc/runlevel.conf, preventing the scripts from being executed.
The lines are: #20 0,1,6 2,3,4,5 /etc/init.d/nvidia-kernel #20 0,1,6 2,3,4,5 /etc/init.d/nvidia-glx-legacy-96xx #20 0,1,6 2,3,4,5 /etc/init.d/nvidia-glx
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