FailsafeX is handy by running Ubuntu in a failsafe graphics mode, should you have issues with your graphics card or if Ubuntu keeps booting to a black screen Fsck will check for file system errors.

I check system logs first: journalctl -p 3 -xb. That shows critical errors from the last boot. If the freezes started after a kernel update, select an older kernel from the GRUB menu when you boot up.