Glitched Linux Startup/Installation

If you are dealing with a glitched Linux startup or installation, in order to fix it, as per fossfreedom’s and Coldfish’s answers,

Option 1 - fossfreedom

Edit the Grub boot process, press e to edit the kernel displayed, and change the line which has quiet splash to nomodeset quiet splash

For example, before:

recordfail=1
save_env recordfail
set quiet=1
insmod ext2
set root=(hd0,1)
search --no-floppy --fs-uuid --set 904bf39-9234
linux /boot/vmlinuz-2.6.31-9 root=UUID=904bf39-9234 ro quiet splash
initrd /bood/initrd.img-2.6.31-9-generic

And after:

recordfail=1
save_env recordfail
set quiet=1
insmod ext2
set root=(hd0,1)
search --no-floppy --fs-uuid --set 904bf39-9234
linux /boot/vmlinuz-2.6.31-9 root=UUID=904bf39-9234 ro nomodeset quiet splash
initrd /bood/initrd.img-2.6.31-9-generic

and exit to boot.

Option 2

Otherwise, you can login via Safe Mode, and edit your /etc/default/grub with

sudo vim /etc/default/grub

and add nomodeset to GRUB_CMDLINE_LINUX_DEFAULT

GRUB_DEFAULT=0
GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nomodeset"
GRUB_CMDLINE_LINUX=""

Save, and update your Grub with

sudo update-grub