My LUKS-encrypted Ubuntu 17.10 install normally would boot to a display that requests a passcode to decrypt the drive and then would boot to the Ubuntu login display. Instead it is now booting just to a black display. I have tried booting it to GRUB by pressing Right Shift but it then just displays GRUB loading. and freezes. I have tried the Alt+←, Alt+→ trick mentioned here, which is listed under the heading "LUKS encryption", to try to get a terminal LUKS dialog for the decryption passcode but this doesn't do anything, and the black display remains, so the solution presented there doesn't work. I can boot to a live USB Ubuntu distribution but I don't know what to do from that.
How can I approach this problem further?
EDIT: After a number of attempts at rebooting (which changing nothing manually) they system eventually booted successfully. I have no idea why increasing the number of boot attempts or letting time pass should be able to fix a problem like this, and I'd like to understand this. However, following this, I encountered the problem again (after Ubuntu froze) and again am seeing the black screen on boot.
While the booting was working this time, I followed the suggestion of David Foerster and managed to record a Boot-Info log from when the boot was succeeding and then subsequently managed to record a Boot-Info log from when the boot was just going to the black screen.
I have compared these logs and nothing jumps out at me but perhaps a more trained eye will see something that I don't.
