keyboard mouse working fine until 3rd attempt at incorrect password mint virtualbox
 

Had to re-enter my Mint virtualbox password, tried 2 times incorrectly, on the third, it wouldn't let me use the keyboard or the mouse to click into the empty password box to start typing. Otherwise mouse and keyboard was working just fine before that.

Little icons on bottom right of virtual box screen say:
Mouse Integration (MI) is ON
Keyboard is Captured

I found that if my computer goes to sleep the guest may or may not "recover" correctly.
Sometimes I can enter a password at the login prompt but then the desktop is frozen.
If the desktop is frozen I can usually use ssh to login from the host and reboot which is easiest and fastest way to "recover"
And last the guest complete crashes and I have to just close it and restart. Knock on wood the filesystem has never been completely corrupted that a fsck will not repair it.

Check in case the Caps Lock or the Number Lock have been turned on when coming back from screen blanking.