Hello I've got last years Macbook and I decided to try the MacOS Sierra Beta. It prompted me to update to Beta 5 which I did. Now the laptop hangs on loading at the black screen with the apple logo (I've uploaded the picture). 1. I've tried resetting NVRAM that does not work. 2. Safe mode did not work either. 3. Holding shift on start up does not work. I'm at the end of my tether I really need to do college work, I'm just happy to wipe the thing and get it back to El Capitan. Please could a kind soul help me out? I'm really in a pickle here I've got loads of work to sort out and then this happens. I will not be trying any Beta again after this upsetting incident.