The latest kernels have moved the video mode setting into the kernel. So all the programming of the hardware specific clock rates and registers on the video card happen in the kernel, rather than in the X driver when the X server starts.

This makes it possible to have high-resolution nice looking splash (boot) screens, and flicker-free transitions from boot splash to login screen.

Unfortunately, on some cards this doesn't work properly and you end up with a black screen. Other problems may be a big boot delay, sometimes coupled with a loss of the configured desktop wallpaper. In particular, some closed non-free Nvidia drivers appear to be affected.

Add the nomodeset parameter, which instructs the kernel to not load video drivers and use BIOS modes instead, until X is loaded.

This has no negative side effects: only your boot process will be a bit less beautiful. The end result (your graphical desktop) will be fine, because it's totally unaffected by nomodeset.

Change the line:

/etc/default/grub

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

to

/etc/default/grub

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nomodeset"

sudo update-grub

Now reboot.