I am hoping someone can help me trouble shoot my failed beta install. I have not been able to launch the computer at all since downloading and initially installing Sierra. I did try using the option key to select my external backup drive, and connecting to wifi. But I am not able to get to any other screens successfully. I've seen a single white no signal, a large symbol with a lighting bolt arrow, and a text screen in multiple languages saying the system shut down because of an error and will restart. The main screen I think has the most information is one I don't know how to interpret. But it gives diagnostics. I appreciate the help!