Black Screen During Upgrade Installation

[G_M_Slater]

I am in the process of upgrading from 14.04 to 15.04. The upgrade process was about half-way complete, then the screen went black. The monitor light is on (green) so it is not in a sleep mode. Also, the activity lights on the front of my computer lead me to believe that it is not frozen. I have an NVIDIA video card, so I have experienced the black screen after installing an upgrade before, and am familiar with resolving the issue. I have never had a black screen problem during an upgrade installation though. I am not sure how best to handle it. If I force a reboot will it completely destroy everything, or will the upgrade resume where it left off?

[G_M_Slater]

Derp... Hitting the Enter key restored the display. Upgrade is still installing. Weird that the monitor was not in sleep mode and/or that moving the mouse did nothing....