OS not booting in VirtualBox

[catgrep]

I hadn't run my LinuxLite VM in several months, so when I booted up, there were a lot of updates.  I installed all the updates and rebooted, now I get a black screen and a blinking cursor before it loads the logon screen and will go no further.

Is there a keyboard shortcut to show the bootloader menu or enter a safe/recovery mode so I can restore from a snapshot?  Any help recovering from this catastrophe is greatly appreciated.