Vivid Vervet upgrade mess - flickering

I upgraded to Ubuntu 15.04 which was just released. After reboot, I get as far as the login screen but it only appears for a second, then it goes to an infinite loop of screen flickering. How could I fix it?

Here is a video of what I'm seeing: https://youtu.be/NCtCw267v8Y

(The tag "Nvidia" is added to this question as that is, or at least was, my graphics driver.)

Note that switching to upstart does not fix this, nor am I able to enter the command line with ctrl+alt+f2.

Update: when I boot with recovery mode, /var/log/Xorg.0.log is empty, and I can at least enter my password (which in normal mode is impossible) but then it starts the same flickering, see this second video recording: https://youtu.be/AdOqBKPnUKA

Valid workaround: go to recovery mode, open a root shell, get list of relevant packages with dpkg -l | grep -i nvidia and remove them all with apt-get remove --purge [package] (for me, they were versions 340 and 331 while the one nvidia itself recommends me - 350 - is not in any ubuntu package)

Solution: upgrade your kernel like this.

I had a similar issue where the normal boot sequence got into a repeated failure pattern like your posted video shows. To be sure you can look at the log file /var/log/Xorg.0.log. In my case, I was able to boot into recovery mode, drop to a root shell, then install a different nvidia driver. In my case, nvidia-340 was installed after the upgrade to 15.04, and upgrading to nvidia-346 fixed it.

In case it helps, here are the steps I followed to fix this.
Problem booting after updating from Ubuntu 14.10 to 15.04

Good luck.

Dennis