Yh, this can happen when using HDMI input. Try just turning the PS3 on, keeping the power button pressed until you hear first beep. If it still doesn't work, try doing it again, but keep it pressed till 2 beeps (recovery mode).
to fix this use the original connection that came with the ps3 you will then get video and it is in the factory mod if it turned off by itself just use the original video connection and you should get video then just change it back to hdmi connection after the update finishes hope this helps. If this dosent work call sony at 1-800-345-7669 and ask for help this is their customer service press 0 to speak to a person right away.
Are you sure you didn't panic while it was installing? I know when I update my 60gb it blacks out at 85% on the download and then installs and then blanks out at like 80% during the install. Every time I get afraid that my machine was crapping out or something.