Cannot load X 1.16.4 after installing GTX 950 on Debian Jessy


I have just replaced a GT 710 with a GTX 950.  I had previously been using the nVidia driver downloaded via apt (following https://linuxconfig.org/nvidia-geforce-driver-installation-on-debian-jessie-linux-8-64bit).  It worked fine.

After physically switching the cards, I removed /etc/X11/xorg.conf and regenerated it with nvidia-xconfig.

Now X will not start up:


I have tried nvidia-bug-report.sh but it hangs without creating a log.

I've tried removind the driver with apt-get remove --purge nvidia-driver and reinstalling.

If I remove xorg.conf I can still start X at 1024x768, without the nvidia driver.