There can be a situation where you are updating the software of your Mac computer and suddenly screen goes Black, this instruction page will help you to resolve the issue. The main reason behind black screen is network connection interruption. So you have to update it again or restore operating system in case update does not work.
Step 1: If you have OS X 10.6 or later version then firstly you need to shut down machine. Hold the Command and R. Keep holding the buttons and press the power button. Machine will go in recovery mode.
Step 2: Now, choose the option “reinstall mac OS X”. It will download and restore whole OS X. Alternately, you can choose ‘TIME MACHINE’ option if you have machine back up.
Step 3: If you are not able to reinstall OS from recovery mode then you need to have an installation disk of OSX 10.5. For startup process, press option and power button. Select installation disk and follow the instructions to install the OS. You can now try updating the software.